Absorbent composites exhibiting stepped capacity behavior

ABSTRACT

An absorbent composite includes a water-insoluble fibrous matrix, a superabsorbent polymer composition that has an initial absorbent capacity of at least about 5 grams of saline per gram of superabsorbent polymer composition; and a first triggering mechanism having a first release time of between about 5 and 60 minutes, where the superabsorbent polymer composition has a second absorbent capacity that is at least about 25 % greater than the first absorbent capacity as measured by the mCRC Test.

BACKGROUND

Articles, such as absorbent articles, are useful for absorbing manytypes of fluids, including fluids secreted or eliminated by the humanbody. Superabsorbent polymers (SAPs) are frequently used in absorbentarticles to help improve the absorbent properties of such articles. SAPsare generally polymer based and are available in many forms, such aspowders, granules, microparticles, films and fibers, for example. Uponcontact with fluids, such SAPs swell by absorbing the fluids into theirstructures. In general, SAPs can absorb fluids insulted into sucharticles, and can retain such fluids to help prevent leakage and to helpprovide a dry feel even after fluid insult. Superabsorbent materials areoften combined with water-insoluble fibers to create an absorbentcomposite for use in an absorbent core of an absorbent article.

There is a continuing effort to improve the performance of absorbentarticles, especially at high levels of fluid saturation, to therebyreduce the occurrence of leakage and to improve fit and comfort. This isparticularly significant when such articles are subjected to repeatedfluid insults during use. This has become an increasing challenge asrecent efforts in absorbent article design have generally focused onusing higher concentrations of superabsorbent material and less flufffiber to make the absorbent structures thinner and more flexible.However, notwithstanding the increase in total absorbent capacityobtained by increasing the concentration of superabsorbent material,such absorbent articles may still nevertheless leak during use. Suchleakage may in part be the result of the absorbent core of an articlehaving a high wet bulk in the fluid insult target zone. A high wet bulkcan lead to cracking or fluid being squeezed out of the composite due tohigher pressure caused by the swelling in the target zone, as well asgeneral discomfort by the user. Therefore, there is a need for anabsorbent composite which provides a reduced wet bulk in the target zoneas compared to composites utilizing conventional SAPs, while generallymaintaining fluid intake rate performance.

In addition, such high wet bulk may in part be the result of theabsorbent composite having an insufficient fluid distribution. Poorfluid distribution decreases the full utility efficiency of absorbentcomposites as not all the superabsorbent material is absorbing liquid,particularly in areas located outside of the target zone. Fluiddistribution in an absorbent composite is generally dependent on theamount of free liquid available for distribution, the structure andmaterials of the absorbent composite, and a time factor. ConventionalSAPs tend to swell in the insult target zone at a moderate rate untileither an entire fluid insult rate has been consumed, or until the SAPhas reached its saturation point. The result is an absorbent compositethat has a high wet bulk and typically does not provide desirable fluiddistribution within an absorbent article. Therefore, there is a need foran absorbent composite which provides improved fluid distribution withinan absorbent article as compared to composites utilizing conventionalSAPs, while generally maintaining fluid intake rate performance.

SUMMARY

In response to the needs discussed above, an absorbent composition ofthe present invention comprises a superabsorbent polymer compositionhaving an initial absorbent capacity of at least about 5 grams of saline(i.e., 0.9 wt % aqueous sodium chloride solution) per gram ofsuperabsorbent polymer composition, and a first triggering mechanism,which may optionally be encapsulated, having a first release time ofbetween about 5 and 60 minutes, where the superabsorbent polymercomposition has a second absorbent capacity that is at least about 25%greater than the first absorbent capacity as measured by the ModifiedCentrifuge Retention Capacity (mCRC) Test. In further aspects, theabsorbent composition further comprises a second triggering mechanism,which may optionally be encapsulated, having a second release time ofbetween about 10 and 120 minutes and at least about 5 minutes longerthan the first release time, where the superabsorbent polymercomposition has a third absorbent capacity that at least about 25%greater than the second absorbent capacity as measured by the mCRC Test.In other aspects, the absorbent composition of further comprises a thirdtriggering mechanism, which may optionally be encapsulated, having athird release time of between about 15 and 180 minutes and at leastabout 5 minutes longer than the second release time, where thesuperabsorbent polymer composition has a fourth absorbent capacity thatis at least about 25% greater than the third absorbent capacity asmeasured by the mCRC Test. In still other aspects, the absorbentcomposition further comprises a fourth triggering mechanism, which mayoptionally be encapsulated, having a fourth release time of betweenabout 20 and 240 minutes and at least about 5 minutes longer than thethird release time, where the superabsorbent polymer composition has afifth absorbent capacity that is at least about 25% greater than thefourth absorbent capacity as measured by the mCRC Test.

In some aspects, the absorbent composition has a swelling rate that isat least about 20% greater than the swelling rate of a conventionalsuperabsorbent material as measured by the Swelling Rate Test, such asat least about 50% greater or at least about 100% greater than theswelling rate of a conventional superabsorbent material as measured bythe Swelling Rate Test.

In some aspects of the present invention, an absorbent compositecomprises a water-insoluble fibrous matrix, a superabsorbent polymercomposition having an initial absorbent capacity of at least about 5grams saline per gram of superabsorbent polymer composition; and a firsttriggering mechanism, which may optionally be encapsulated, having afirst release time of between about 5 and 60 minutes, where thesuperabsorbent polymer composition has a second absorbent capacity thatis at least about 25% greater than the first absorbent capacity asmeasured by the mCRC Test. In other aspects, the absorbent compositefurther comprises a second triggering mechanism, which may optionally beencapsulated, having a second release time of between about 10 and 120minutes and at least about 5 minutes longer than the first release time,where the superabsorbent polymer composition has a third absorbentcapacity that is at least about 25% greater than the second absorbentcapacity as measured by the mCRC Test. In still other aspects, theabsorbent composite further comprises a third triggering mechanism,which may optionally be encapsulated, having a third release time ofbetween about 15 and 180 minutes and at least about 5 minutes longerthan the second release time, where the superabsorbent polymercomposition has a fourth absorbent capacity that is at least about 25%greater than the third absorbent capacity as measured by the mCRC Test.In yet another aspect, the absorbent composite further comprises afourth triggering mechanism, which may optionally be encapsulated,having a fourth release time of between about 20 and 240 minutes and atleast about 5 minutes longer than the third release time, where thesuperabsorbent polymer composition has a fifth absorbent capacity thatis at least about 25% greater than the fourth absorbent capacity asmeasured by the mCRC Test.

In some aspects, the absorbent composite includes a superabsorbentpolymer composition having a swelling rate that is at least about 20%greater than the swelling rate of a conventional superabsorbentmaterial, such as at least about 50% greater or at least about 100%greater than the swelling rate of a conventional superabsorbent materialas measured by the Swelling Rate.

In some aspects, an absorbent article comprises an absorbent core thatincludes a superabsorbent polymer composition having an initialabsorbent capacity of at least about 5 grams saline per gram ofsuperabsorbent polymer composition, and a first triggering mechanism,which may optionally be encapsulated, having a first release time ofbetween about 5 and 60 minutes, where the superabsorbent polymercomposition has a second absorbent capacity that is at least about 25%greater than the first absorbent capacity as measured by the mCRC Test.In other aspects, the absorbent article comprises a topsheet and abacksheet, where the absorbent core is disposed between the topsheet andthe backsheet.

In some aspects, the absorbent core comprises at least about 30% byweight of the superabsorbent polymer composition. In other aspects, theabsorbent core comprises about 60% to about 95% by weight of thesuperabsorbent polymer composition.

In some aspects, the absorbent core further comprises fluff. In otheraspects, the absorbent core comprises layers. In still other aspects, atleast one of the layers of the absorbent core comprises substantiallyonly the superabsorbent polymer composition of the present invention andat least one of the layers comprises substantially only fluff. In yetother aspects, the absorbent core further comprises a surfactant.

In some aspects, the absorbent article is selected from personal careabsorbent articles, health/medical absorbent articles,household/industrial absorbent articles and sports/constructionabsorbent articles.

Numerous other features and advantages of the present invention willappear from the following description. In the description, reference ismade to exemplary embodiments of the invention. Such embodiments do notrepresent the full scope of the invention. Reference should therefore bemade to the claims herein for interpreting the full scope of theinvention. In the interest of brevity and conciseness, any ranges ofvalues set forth in this specification contemplate all values within therange and are to be construed as support for claims reciting anysub-ranges having endpoints which are real number values within thespecified range in question. By way of a hypothetical illustrativeexample, a disclosure in this specification of a range of from 1 to 5shall be considered to support claims to any of the following ranges:1-5; 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.

FIGURES

The foregoing and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims and accompanying drawings where:

FIG. 1 is a side view of the test apparatus employed for the AbsorbencyUnder Load Test;

FIG. 2 is a top view of the test apparatus employed for the Fluid IntakeRate Test;

FIG. 3 is a cross-sectional side view taken along line 5-5 of the testapparatus employed for the Fluid Intake Rate Test shown in FIG. 2;

FIG. 4 is a side view of an apparatus employed for the Swell Rate Test;

FIG. 5 is a perspective view of one embodiment of an absorbent articlethat may be made in accordance with the present invention;

FIG. 6 is a plan view of the absorbent article shown in FIG. 5 with thearticle in an unfastened, unfolded and laid flat condition showing thesurface of the article that faces the wearer when worn and with portionscut away to show underlying features;

FIG. 7 is a schematic diagram of one version of a method and apparatusfor producing an absorbent core;

FIG. 8 is a cross-sectional side view of a layered absorbent coreaccording to the present invention;

FIG. 9 is a perspective view of an absorbent article according to oneaspect of the present invention.

FIG. 10A is a cross-section side view of an absorbent bandage of thepresent invention;

FIG. 10B is a top perspective view of an absorbent bandage of thepresent invention;

FIG. 11 is a top perspective view of an absorbent bed or furniture linerof the present invention;

FIG. 12 is a perspective view of an absorbent sweatband of the presentinvention;

FIG. 13 is an absorbent system in the form of a pad in a laid flatcondition;

FIG. 14 is a graphical representation of fluid distribution after afirst fluid insult and hold time;

FIG. 15 is a graphical representation of fluid distribution after asecond fluid insult and hold time;

FIG. 16 is a graphical representation of fluid distribution after a3^(rd) fluid insult and hold time; and

FIG. 17 is a graphical representation of stepped capacity behavior.

Repeated use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

Test Methods

Modified Centrifuge Retention Capacity (mCRC) Test

This test determines the free swelling capacity of a hydrogel-formingpolymer while in a limited liquid condition. The resultant retentioncapacity is stated as grams of liquid retained per gram weight of thesample (g/g). In this method, 0.2000±0.0050 g of dry superabsorbentpolymer composition particles of size fraction 300 to 600 μm areinserted into a teabag. The superabsorbent polymer composition particlescan be pre-screened with, for example, a RO-TAP Mechanical Sieve ShakerModel B available from W. S. Tyler, Inc., having a place of businesslocated in Mentor, Ohio, U.S.A. Sieving is conducted for 10 minutes. Aheat-sealable tea bag material, such as that available from DexterCorporation (having a place of business in Windsor Locks, Conn. U.S.A.)as model designation 1234T heat sealable filter paper works well formost applications. The bag is formed by folding a 5-inch by 3-inch(12.7-cm×7.6-cm) sample of the bag material in half and heat-sealing twoof the open edges to form a 2.5-inch by 3-inch (6.4-cm×7.6-cm)rectangular pouch. The heat seals are about 0.25 inches (0.6 cm) insidethe edge of the material.

After the sample is placed in the pouch, the remaining open edge of thepouch is also heat-sealed. Empty bags can also be made to serve ascontrols. 10 ml of saline solution (i.e., 0.9 wt % aqueous sodiumchloride) is placed into a container, sufficiently large to permit theteabag to lay flat, yet small enough to prevent the saline fromspreading over an excessively large area. The container for the salineshould have a bottom cross-sectional area between 8 in²-15 in² (52cm²-97 cm²). An appropriate container is a 100 mm diameter Petri dish,catalog number 25384-056 available from VWR International (having aplace of business located in West Chester, Pa., U.S.A.). The teabag isplaced in the saline solution for a fixed period of time (see below),making sure that the bags are held down until they are completelywetted. Following the fixed period of immersion in saline, the teabag iscentrifuged for 3 minutes at 290G-force with a variance from about 286to about 292G-force). G-force is defined as a unit of inertial force ona body that is subjected to rapid acceleration or gravity, equal to 32ft/sec/sec at sea level.

The absorbed quantity of saline solution is determined by measuring theweight of the teabag. The amount of solution retained by thesuperabsorbent polymer composition sample, taking into account thesolution retained by the bag itself, is the modified CentrifugeRetention Capacity (mCRC) of the superabsorbent polymer composition atthe fixed immersion time, expressed as grams of fluid per gram ofsuperabsorbent polymer composition. More particularly, the modifiedcentrifuge retention capacity is determined by the following equation:[sample and bag wt. after centrifuge]−[empty bag wt. aftercentrifuge]−[dry sample wt.]

-   -   [dry sample wt.]

In order to fully characterize the free swelling capacity of thesuperabsorbent polymer composition under limited liquid conditions,multiple samples of superabsorbent material need to be prepared asdescribed above and placed into multiple teabags. Each teabag must beimmersed in its own 10 ml of saline solution. The time an individualsample is immersed in the saline solution should range from 5 minutes to240, at 5 minute intervals. Each immersion time can be done with onlyone replicate.

Typical stepped capacity swelling behavior of this invention is shownhypothetically in FIG. 17. Data points would be those capacity valuesmeasured at specific immersion times as discussed above. The first(initial) absorbent capacity can be seen as the first plateau of theswelling curve, as indicated in FIG. 17. Likewise the second absorbentcapacity can be seen as the second plateau of the swelling curve, asindicated in FIG. 17. Subsequent absorbent capacities can be determinedin a similar manner.

Absorbency Under Load Test (AUL)

The Absorbency Under Load (AUL) Test measures the ability of thesuperabsorbent polymer composition to absorb saline solution at roomtemperature (test solution) while the material is under a 0.9 psi load.The apparatus for testing AUL consists of:

-   -   An AUL assembly including a cylinder, a 4.4 g piston, and a 317        gram weight. The components of this assembly are described in        additional detail below.    -   A flat-bottomed plastic tray that is sufficiently broad to allow        the glass frits to lay on the bottom without contact with the        tray walls. A plastic tray that is 9 inches by 9 inches (22.9        cm×22.9 cm), with a depth of 0.5 to linch (1.3 to 2.5 cm) is        commonly used for this test method.    -   A 12.5 cm diameter sintered glass frit with a ‘C’ porosity        (25-50 microns). This frit is prepared in advance through        equilibration in saline. In addition to being washed with at        least two portions of fresh saline, the frit must be immersed in        saline for at least 12 hours prior to AUL measurements.    -   Whatman Grade 1, 12.5 cm diameter filter paper circles.    -   A supply of saline (0.9% sodium chloride in distilled water, by        weight).

Referring to FIG. 1, the cylinder 412 of the AUL assembly 400 used tocontain the superabsorbent polymer composition 410 is made from one-inch(2.54 cm) inside diameter clear acrylic tubing machined-out slightly tobe sure of concentricity. After machining, a 400 mesh stainless steelwire cloth 414 is attached to the bottom of the cylinder 412 using anappropriate solvent that causes the screen to be securely adhered to thecylinder. Care must be taken to avoid excess solvent migrating into theopen portions of the screen and reducing the open area for liquid flow.Acrylic solvent Weld-On 4 from IPS Corporation (having a place ofbusiness in Gardena, Calif., U.S.A.) is a suitable solvent. A solderingiron can be utilized to touch up the seal if unsuccessful or if itbreaks. Care must be taken to maintain a flat smooth bottom and notdistort the inside of the cylinder 412.

The 4.4 g piston 416 is made from 1-inch (2.5 cm) diameter solidmaterial (e.g., PLEXIGLAS) and is machined to closely fit withoutbinding in the cylinder 412.

A 317 gram weight 418 is used to provide a 62,053 dyne/cm² (about 0.9psi) restraining load. The weight is a cylindrical, 1 inch (2.5 cm)diameter, stainless steel weight that is machined to closely fit withoutbinding in the cylinder.

Unless specified otherwise, a sample 410 corresponding to a layer of atleast about 300 gsm (0.16 g) of superabsorbent polymer particles isutilized for testing the AUL. The sample 410 is taken fromsuperabsorbent polymer composition particles that are pre-screenedthrough U.S. standard #30 mesh and retained on U.S. standard #50 mesh.The superabsorbent polymer composition particles can be pre-screenedwith, for example, a RO-TAP Mechanical Sieve Shaker Model B availablefrom W. S. Tyler, Inc., Mentor, Ohio, U.S.A. Sieving is conducted for 10minutes.

The desired amount of the sample of sieved superabsorbent polymercomposition particles 410 (about 0.16 g) is weighed out on a weigh paperand evenly distributed on the wire cloth 414 at the bottom of thecylinder 412. The weight of the superabsorbent polymer composition inthe bottom of the cylinder is recorded as ‘SA,’ for use in the AULcalculation described below. Care is taken to be sure no superabsorbentpolymer composition particles cling to the wall of the cylinder. Theinside of the cylinder 412 is wiped with an antistatic cloth prior toplacing the superabsorbent polymer composition particles 410 into thecylinder 412. After carefully placing the 4.4 g piston 412 and 317 gweight 418 on the superabsorbent polymer composition particles 410 inthe cylinder 412, the AUL assembly 400 including the cylinder, piston,weight, and superabsorbent polymer composition is weighed, and theweight is recorded as weight ‘A’.

The sintered glass frit 424 (described above) is placed in the plastictray 420, with saline 422 added to a level equal to that of the uppersurface of the glass frit 424. A single circle of filter paper 426 isplaced gently on the glass frit, and the AUL assembly 400 with thesuperabsorbent polymer particles 410 is then placed on top of the filterpaper 426. The AUL assembly 400 is then allowed to remain on top of thefilter paper 426 for a test period of one hour, with attention paid tokeeping the saline level in the tray constant. At the end of the onehour test period, the AUL apparatus is then weighed, with this valuerecorded as weight ‘B.’

The AUL(0.9 psi) is calculated as follows:AUL(0.9 psi)=(B−A)/SA

wherein:

A=Weight of AUL Unit with dry SAP;

B=Weight of AUL Unit with SAP after 60 minutes absorption; and

SA=Actual SAP weight.

A minimum of two tests are performed and the results are averaged todetermine the AUL value under 0.9 psi load. The samples are tested atabout 23° C. and about 50% relative humidity.

Fluid Intake Rate Test

The Fluid Intake Rate (FIR) Test determines the amount of time requiredfor an absorbent structure to take in (but not necessarily absorb) aknown amount of test solution. A suitable apparatus for performing theFIR Test is shown in FIGS. 2 and 3 and is generally indicated at 200.The test apparatus 200 comprises an assembly, generally indicated at202.

The assembly 202 comprises a generally 6 inch (15.2 cm) by 10 inch (25.4cm) rectangular plate 208 constructed of a transparent material such asPLEXIGLAS (available from Degussa A G, a business having offices locatedin Dusseldorf, Germany) and having a central opening 210 formed therein.A cylinder (fluid delivery tube) 212 having an inner diameter of aboutone inch (2.5 cm) is secured to the plate 208 at the central opening 210and extends upward substantially perpendicular to the plate. The centralopening 210 of the plate 208 should have a diameter at least equal tothe inner diameter of the cylinder 212 where the cylinder 212 is mountedon top of the plate 208. However, the diameter of the central opening210 may instead be sized large enough to receive the outer diameter ofthe cylinder 212 within the opening so that the cylinder 212 is securedto the plate 208 within the central opening 210.

The weight of the assembly 202 (e.g., the plate 208 and cylinder 212) isapproximately 465 grams to apply slight pressure on the absorbent sampleduring the FIR Test.

To run the FIR Test, an absorbent sample 207 being cut to a generallyhour-glass pad shape typically used in disposable absorbent products,such as diapers, is weighed and the weight is recorded in grams.Approximate dimensions of the pad are a length of 15 inches (38 cm) witha width of 3 inches (7.6 cm) in the mid-section and a width of 4.75inches (12 cm) at the ends. The assembly 202 is placed over the sample207 such that the center of the cylinder 212 is generally located 4.5inches (11.4 cm) from the front edge of the sample 207, and centered inthe lateral direction. 45 grams of test solution (0.9 weight percentsolution of sodium chloride in distilled water at room temperature, oran alternative based on the specific system being tested) is poured intothe top of the cylinder 212 and allowed to flow down into the absorbentsample 207. A stopwatch is started when the first drop of solutioncontacts the sample 207 and is stopped when the liquid ring between theedge of the cylinder 212 and the sample 207 disappears. The reading onthe stopwatch is recorded to two decimal places and represents theintake time (in seconds) required for the first 45 gram insult to betaken into the absorbent sample 207. Three minutes after the first 45gram insult, an additional 25 grams of test solution is poured into thetop of the cylinder 212 and allowed to flow down into the absorbentsample 207. The time required for this 25 gram insult to enter thesample is not recorded. The test solution for the 25 gram insult may bethe same or different than the test solution used for the first 45 graminsult. The combination of the 45 gram insult, followed three minuteslater by a 25 gram insult, together represents the first insult.

A time period of 15 minutes, from the beginning of the first 45 graminsult described above, is allowed to elapse, after which a secondinsult series similar to the first insult is poured into the top of thecylinder 212 and again the intake time is measured as described above.The test solution for the second insult series may be the same ordifferent than the test solution for the first insult series. 15 minutesafter the beginning of the second insult series, the procedure describedabove is repeated for a third insult series. An intake rate (inmilliliters/second) for each of the three insults is determined bydividing the amount of solution used for the first 45 gram portion ofeach insult (45 grams) by the intake time measured for the correspondinginsult.

At least three samples of each absorbent test are subjected to the FIRTest and the results are averaged to determine the intake rate.

Fluid Distribution Test

This test utilizes x-ray imaging to determine the amount of fluidlocated in various locations of the absorbent system. X-ray imaging isknown in the art as discussed, for example, in an article entitled“Fluid Distribution: comparison of X-ray Imaging Data” by David F. Ring,Oscar Lijap and Joseph Pascente in Nonwovens Worldmagazine, summer 1995,at pages 65-70, which is incorporated herein by reference in a mannerthat is consistent herewith. Generally, this procedure compares the greyscale x-ray images of a wet and dry sample in order to calculate theliquid content at various locations. Such x-ray systems are available,for example, from Precision X-ray Inc., having a place business locatedat 31 Business Park Drive, Branford, Conn., U.S.A. as model no. 10561 HF100 with enclosure. This system may use image analysis software fromOptimus Inc., having a place of business located at Ft. Collins, Colo.,U.S.A. as BIO-SCAN OPTIMATE S/N OPM4101105461 version 4.11, orequivalent. The x-ray system is operated with an exposure time of 2seconds, with a tube voltage of 50 Kv and current of 12 mA.

When a Fluid Distribution analysis is conducted in conjunction withother tests, such as the Fluid Intake Rate Test described above, thex-ray imaging should be conducted at a specific time. The sample shouldremain in the same gravitational orientation as used in the Fluid IntakeRate Test (i.e., horizontal). When used in conjunction with the FluidIntake Rate Test, x-ray images are taken just prior to the next insultseries. For example, x-ray images for the “first hold” (i.e., the timebetween or after each fluid insult) are taken just prior to the secondinsult series, typically within 2 minutes of the next insult series.

Additionally, a measurement of the thickness of the absorbent sample maybe made before or after the x-ray image is taken. The thicknessmeasurement may be taken at the region of the pad which aligns with thefluid delivery tube from the upper assembly described in the FluidIntake Rate Test. Thickness measurements can be made with well knowndevices, such as a SONY DIGITAL INDICATOR, model U30A-F, available fromSony Precision Technology Inc., having a place of business located inJapan. Pressure applied to the sample during thickness measurementshould be less than 0.1 psi.

Swelling Rate Test

This test measures the rate of swelling of a superabsorbent materialwith a given fluid. 0.160 grams of superabsorbent material is confinedwithin a 5.07 cm² area Absorbency Under Load cylinder (described abovein the Absorbency Under Load Test procedure) under a nominal pressure of0.3 psi (2.1 kPa). The sample is allowed to absorb the test fluid from adish containing excess fluid. At known time intervals, a sample isweighed after a vacuum apparatus operating at 26 inches of mercuryvacuum has removed any excess interstitial fluid within the cylinder.This weight versus time data is reduced to a single diffusioncoefficient value for the superabsorbent material. The diffusioncoefficient is an inherent property of a specific superabsorbentmaterial that characterizes the diffusion rate between thesuperabsorbent and a test fluid. A description of superabsorbentdiffusion can be found in “Kinetics of One-dimensional Gel Swelling andCollapse for Large Volume Change” by J. Singh and M. E. Weber, ChemicalEngineering Science Vol. 51 No.19 pp 4499-4508 (1996), which isincorporated herein by reference in a manner that is consistentherewith. The model is based upon Fick's first law of diffusion whereflux is proportional to the concentration gradient.

Equipment required to carry out the Swelling Rate Test includes thefollowing:

-   -   Electronic balance, accurate to 0.001 gram, 100-gram minimum        capacity.    -   With reference to FIG. 4, a Swell Rate Apparatus 910 that        includes an AUL assembly 925 having a cylinder 920, a piston 930        and weight 990 as described in the Absorbency Under Load (AUL)        Test method described above, except the 317 gram weight        mentioned in the AUL Test is replaced with a 100 gram weight,        available from VWR International (having a place of business        located in West Chester, Pa., U.S.A.) as part number 12727-141,        or equivalent.    -   The Swell Rate apparatus 910 which also includes an AUL chamber        940 used to remove interstitial liquid which is picked up during        the swelling of the superabsorbent sample 950. The unit is        similar to a demand absorbency tester (DAT). This test apparatus        is similar to a GATS (gravimetric absorbency test system),        available from M/K Systems, (having a place of business located        in Danners, Mass., U.S.A.), as well as the system described by        Lichstein at pages 129-142 of the INDA Technological Symposium        Proceedings, March 1974, which is incorporated herein by        reference in a manner that is consistent herewith. A ported disk        935 is also utilized having ports confined within a 2.5        centimeter diameter area.    -   Fluid bath—Petri dish, plastic weighing dish or similar which        can hold an excess of fluid.    -   Stainless steel wire or plastic mesh screen with large open        area, such as an 8 mesh plastic screen.    -   Vacuum source—aspirator, house vacuum line or vacuum pump.    -   Side arm flask 960 (FIG. 4) fitted with a rubber stopper 945 and        tube 955 in the top of the flask.    -   Rubber or plastic tubing 970 (FIG. 4).    -   Timer, capable of reading 120 minutes by one-second intervals.    -   Paper toweling or tissue.    -   Anti-static cloth, for example from Ilford Photo Corp. (having a        place of business located in Wyckoff, N.J., U.S.A.), part number        203547 or equivalent.    -   A distribution of particle sizes representative of the bulk        superabsorbent material should be used for testing. This        typically requires the use of a spinning riffler. An appropriate        riffler is Model SR 1B available from Microscal Limited (having        a place of business located in London, England). Sufficient        superabsorbent material should be added to the riffler, such        that each separated sample weighs 0.160±0.005 gm.    -   Vacuum apparatus—Using tubing 970, connect between the AUL        chamber 940 and the tube in the top of the side arm flask 960.        Use tubing 970 to connect between the vacuum source (not shown)        and the side arm 980 of the flask 960. The purpose of the side        arm flask 960 is to trap any fluid removed from the sample        before it enters the vacuum system. To improve stability of the        side arm flask 960, it is recommended to attach it to a ring        stand or similarly secure it.    -   Fluid bath—Place a wire mesh (not shown) or similar large mesh        plastic screen in the bottom of a fluid bath dish (not shown).        Position the screen to hold the AUL assembly 925 up from the        bottom of the bath and allow free access of the fluid to the        sample.

To carry out the test, wipe the inside of the AUL cylinder 920 with theanti-static cloth, and weigh the cylinder 920, weight 990 and piston930. Record the weight as CONTAINER WEIGHT in grams to the nearestmilligram.

Slowly pour the 0.16±0.005 gram sample of the superabsorbent material950 into the cylinder 920. Take care to not allow the superabsorbentmaterial to make contact with the sides of the cylinder or it may adhereto the walls of the AUL cylinder.

Weigh the cylinder 920, weight 990, piston 930, and superabsorbent 950and record the value on the balance, as DRY WEIGHT in grams to thenearest milligram.

Gently tap the AUL cylinder 920 until the superabsorbent material 950 isevenly distributed on the bottom of the cylinder. Gently place thepiston 930 and weight 990 into the cylinder 920.

Place the test fluid (0.9 wt % aqueous sodium chloride solution) in thefluid bath with the large mesh screen on the bottom. Simultaneouslystart the timer and place the superabsorbent sample 950 and cylinderassembly 925 onto the screen in the fluid bath. The level in the bathshould be at a height to provide at least a 1 cm positive head above thebase of the cylinder. Gently swirl the sample to release any trapped airand ensure the superabsorbent material is in contact with the fluid.

Two samples at each predetermined time interval must be tested.Suggested time intervals are 30, 120, 300, 600, 1800 and 3600 seconds.

Remove the cylinder 920 from the fluid bath at the designated time andimmediately place the cylinder on the vacuum apparatus (ported disk 935on the top of the AUL chamber 940) and remove excess interstitial fluidfor 10 seconds.

Wipe the exterior of the cylinder with paper toweling or tissue.

Weigh the AUL assembly (i.e., cylinder 920, piston 930 and weight 990),with the superabsorbent material and any absorbed test fluid immediatelyand record the weight as WET WEIGHT in grams to the nearest milligram.Record the corresponding Swelling Time in seconds as well.

The swelling level of the superabsorbent material at the designated timeis calculated by the following formula:(Wet Weight−Dry Weight)/(Dry Weight−Container Weight)=swelling level ofsuperabsorbent material [grams liquid/grams superabsorbent]

Repeat for all time intervals needed. Exact time intervals for theweighing are dependent upon the absorption rate of the superabsorbentmaterial. Generally, at least 6 data points of weight versus time shouldbe taken to complete the rate curve. An initial trial may be required todetermine the time intervals that span a wide enough range of swellinglevels and to determine the appropriate time interval which should beused to represent the saturated capacity of the superabsorbent material.This time interval must be chosen such that the swelling level hasreached a nearly equilibrium swelling level.

Using the recorded times, weights, average superabsorbent particle sizeand the saturated capacity of the superabsorbent the diffusioncoefficient can be calculated by the following method:

At each time interval convert the swelling level of the superabsorbentmaterial in grams liquid /gram superabsorbent material to a fractionalsaturation (based on the saturated capacity of the superabsorbentmeasured at the longest time interval). Then plot the data as fractionalsaturation versus time. Use the diffusion coefficient model found in theSingh and Weber reference mentioned earlier and adjust the diffusioncoefficient from the model until the swelling rate curve from the modelfits the experimental data using well known least square fit methods ortechniques available in publicly available software such as MicrosoftExcel 2003. The diffusion coefficient that best fits the experimentaldata can be referred to as the Swelling Rate of the superabsorbent.

It is noted that particle size determination is well known in the art.One suitable method utilizes a particle size distribution test where asample of superabsorbent material is added to the top of a series ofstacked sieves, each of which has consecutively smaller openings. Thesieves are mechanically shaken for a predetermined time, then the amountof superabsorbent material on each sieve is weighed. The percent ofsuperabsorbent material on each sieve is calculated from the initialsample weight of the superabsorbent material sample.

In the case of a superabsorbent material which exhibits the steppedcapacity behavior of present invention, the swelling rate of eachswelling “step” should be measured separately. The saturated capacityused for each step should be the capacity determined for the swellingstep of interest.

Mannequin Test Procedure

The Mannequin Test procedure involves placing an absorbent article ontoa static mannequin representing the torso of an appropriate sized human.Suitable mannequins can be obtained from Marketing Technology Services,Inc., having a place of business located in Kalamazoo, Mich., U.S.A.Fluid is added to the product by way of tubing running through theinterior of the mannequin. Once liquid leaks from the product, it isdetected by sensors that stop the liquid addition to that product. Theamount of liquid added to the product when it leaks can be determined byweighing the products before and after they are removed from themannequin.

Products can be evaluated for their leakage performance using themannequin test procedure disclosed herein. Saline leakage performance istested on a static mannequin system. The static mannequin system can beused in a forced leakage protocol in which the mannequin remains in thesame position for the evaluation, in this case in the prone position(simulating the condition when the product user is laying on his/herstomach). The mannequin system uses a computer controlled set of valvesand sensors to automatically deliver fluid to a particular mannequin anddetermine when a leakage event has occurred. The amount of liquid addedand the frequency of liquid addition can be controlled. For a particulartest, these conditions can be fixed. When a product has leaked, asindicated by a sensor or visually seeing the leak, it is removed andweighed to determine the amount of fluid that has been absorbed (i.e.load at leak). Optionally, after removal of the products from themannequins, the products can be x-rayed for fluid distribution asdescribed in the Fluid Distribution Test above. Also optionally, foreach product code, data can be reported as an average load at leak, aswell as a cumulative leakage distribution curve.

Definitions

It should be noted that, when employed in the present disclosure, theterms “comprises,” “comprising” and other derivatives from the root term“comprise” are intended to be open-ended terms that specify the presenceof any stated features, elements, integers, steps, or components, andare not intended to preclude the presence or addition of one or moreother features, elements, integers, steps, components, or groupsthereof.

The term “absorbent article” generally refers to devices which canabsorb and contain fluids. For example, personal care absorbent articlesrefer to devices which are placed against or near the skin to absorb andcontain the various fluids discharged from the body.

The term “coform” is intended to describe a blend of meltblown fibersand cellulose fibers that is formed by air forming a meltblown polymermaterial while simultaneously blowing air-suspended cellulose fibersinto the stream of meltblown fibers. The coform material may alsoinclude other materials, such as superabsorbent materials. The meltblownfibers containing wood fibers and/or other materials are collected on aforming surface, such as provided by a foraminous belt. The formingsurface may include a gas-pervious material, such as spunbonded fabricmaterial, that has been placed onto the forming surface.

The term “crosslinked” used in reference to the superabsorbent polymercomposition refers to any means for effectively rendering normallywater-soluble materials substantially water-insoluble but swellable.Such a crosslinking means can include, for example, physicalentanglement, crystalline domains, covalent bonds, ionic complexes andassociations, hydrophilic associations such as hydrogen bonding,hydrophobic associations, or Van der Waals forces.

The term “disposable” is used herein to describe absorbent articles thatare not intended to be laundered or otherwise restored or reused as anabsorbent article after a single use.

The terms “elastic,” “elastomeric,” “elastically”, “extensible” and“elastically extensible” are used interchangeably to refer to a materialor composite that generally exhibits properties which approximate theproperties of natural rubber. The elastomeric material is generallycapable of being extended or otherwise deformed, and then recovering asignificant portion of its shape after the extension or deforming forceis removed.

The terms “fluid impermeable,” “liquid impermeable,” “fluid impervious”and “liquid impervious” mean that fluid such as water or bodily fluidswill not pass substantially through the layer or laminate under ordinaryuse conditions in a direction generally perpendicular to the plane ofthe layer or laminate at the point of fluid contact.

The term “health/medical absorbent articles” includes a variety ofprofessional and consumer health-care products including, but notlimited to, products for applying hot or cold therapy, medical gowns(i.e., protective and/or surgical gowns), surgical drapes, caps, gloves,face masks, bandages, wound dressings, wipes, covers, containers,filters, disposable garments and bed pads, medical absorbent garments,underpads, and the like.

The term “household/industrial absorbent articles” includes constructionand packaging supplies, products for cleaning and disinfecting, wipes,covers, filters, towels, disposable cutting sheets, bath tissue, facialtissue, nonwoven roll goods, home-comfort products including pillows,pads, mats, cushions, masks and body care products such as products usedto cleanse or treat the skin, laboratory coats, coveralls, trash bags,stain removers, topical compositions, pet care absorbent liners, laundrysoil/ink absorbers, detergent agglomerators, lipophilic fluidseparators, and the like.

The terms “hydrophilic” and “wettable” are used interchangeably to referto a material having a contact angle of water in air of less than 90degrees. The term “hydrophobic” refers to a material having a contactangle of water in air of at least 90 degrees. For the purposes of thisapplication, contact angle measurements are determined as set forth inRobert J. Good and Robert J. Stromberg, Ed., in “Surface and ColloidScience—Experimental Methods,” Vol. II, (Plenum Press, 1979), which isincorporated herein by reference in a manner that is consistentherewith.

The term “layer” when used in the singular can have the dual meaning ofa single element or a plurality of elements.

The term “MD” or “machine direction” refers to the orientation of theabsorbent web that is parallel to the running direction of the formingfabric and generally within the plane formed by the forming surface. Theterm “CD” or “cross-machine direction” refers to the directionperpendicular to the MD and generally within the plane formed by theforming surface. Both MD and CD generally define a plane that isparallel to the forming surface. The term “ZD” or “Z-direction” refersto the orientation that is perpendicular to the plane formed by the MDand CD.

The term “meltblown fibers” refers to fibers formed by extruding amolten thermoplastic material through a plurality of fine, usuallycircular, die capillaries as molten threads or filaments into a highvelocity, usually heated, gas (e.g., air) stream which attenuates thefilaments of molten thermoplastic material to reduce their diameter. Inthe particular case of a coform process, the meltblown fiber streamintersects with one or more material streams that are introduced from adifferent direction. Thereafter, the meltblown fibers and othermaterials are carried by the high velocity gas stream and are depositedon a collecting surface. The distribution and orientation of themeltblown fibers within the formed web is dependent on the geometry andprocess conditions. Under certain process and equipment conditions, theresulting fibers can be substantially “continuous,” defined as havingfew separations, broken fibers or tapered ends when multiple fields ofview are examined through a microscope at 10×or 20×magnification. When“continuous” melt blown fibers are produced, the sides of individualfibers will generally be parallel with minimal variation in fiberdiameter within an individual fiber length. In contrast, under otherconditions, the fibers can be overdrawn and strands can be broken andform a series of irregular, discrete fiber lengths and numerous brokenends. Retraction of the once attenuated broken fiber will often resultin large clumps of polymer.

The terms “nonwoven” and “nonwoven web” refer to materials and webs ofmaterial having a structure of individual fibers or filaments which areinterlaid, but not in an identifiable manner as in a knitted fabric. Theterms “fiber” and “filament” are used herein interchangeably. Nonwovenfabrics or webs have been formed from many processes such as, forexample, meltblowing processes, spunbonding processes, air layingprocesses, and bonded-carded-web processes. The basis weight of nonwovenfabrics is usually expressed in ounces of material per square yard (osy)or grams per square meter (gsm) and the fiber diameters are usuallyexpressed in microns. (Note that to convert from osy to gsm, multiplyosy by 33.91.)

The term “particles” when used in conjunction with the term“superabsorbent” refers generally to discrete units. The units cancomprise particles, granules, fibers, flakes, agglomerates, rods,spheres, needles, particles coated with fibers or other additives,pulverized materials, powders, films, and the like, as well ascombinations thereof. The materials can have any desired shape such as,for example, cubic, rod-like, polyhedral, spherical or semi-spherical,rounded or semi-rounded, angular, irregular, etc.

The term “personal care absorbent article” includes, but is not limitedto, absorbent articles such as diapers, diaper pants, baby wipes,training pants, absorbent underpants, child care pants, swimwear, andother disposable garments; feminine care products including sanitarynapkins, wipes, menstrual pads, menstrual pants, panty liners, pantyshields, interlabials, tampons, and tampon applicators; adult-careproducts including wipes, pads such as breast pads, containers,incontinence products, and urinary shields; clothing components; bibs;athletic and recreation products; and the like.

The term “polymer” includes, but is not limited to, homopolymers,copolymers, for example, block, graft, random, and alternatingcopolymers, terpolymers, etc., and blends and modifications thereof.Furthermore, unless otherwise specifically limited, the term “polymer”shall include all possible configurational isomers of the material.These configurations include, but are not limited to isotactic,syndiotactic, and atactic symmetries.

The term “polyolefin” as used herein generally includes, but is notlimited to, materials such as polyethylene, polypropylene,polyisobutylene, polystyrene, ethylene vinyl acetate copolymer and thelike, the homopolymers, copolymers, terpolymers, etc., thereof, andblends and modifications thereof. The term “polyolefin” shall includeall possible structures thereof, which includes, but is not limited to,isotatic, synodiotactic and random symmetries. Copolymers include randomand block copolymers.

Unless otherwise indicated, the term “saline” means a 0.9 wt % aqueoussodium chloride solution.

The term “sports/construction absorbent articles” includes headbands,wrist bands and other aids for absorption of perspiration, absorptivewindings for grips and handles of sports equipment, and towels orabsorbent wipes for cleaning and drying off equipment during use.

The terms “spunbond” and “spunbonded fiber” refer to fibers which areformed by extruding filaments of molten thermoplastic material from aplurality of fine, usually circular, capillaries of a spinneret, andthen rapidly reducing the diameter of the extruded filaments.

The term “stretchable” refers to materials which may be extensible orwhich may be elastically extensible.

The term “superabsorbent” refers to water-swellable, water-insolubleorganic or inorganic materials capable, under the most favorableconditions, of absorbing at least about 5 times their weight, or atleast about 10 times their weight, or at least about 20 times theirweight in an aqueous solution containing 0.9 weight percent sodiumchloride.

The term “target zone” refers to an area of an absorbent core where itis particularly desirable for the majority of a fluid insult, such asurine, menses, or bowel movement, to initially contact. In particular,for an absorbent core with one or more fluid insult points in use, theinsult target zone refers to the area of the absorbent core extending adistance equal to 15% of the total length of the composite from eachinsult point in both directions.

The term “thermoplastic” describes a material that softens when exposedto heat and which substantially returns to a non-softened condition whencooled to room temperature.

The term “% by weight” or “wt %” when used herein and referring tocomponents of the superabsorbent polymer composition, is to beinterpreted as based on the dry weight of the superabsorbent polymercomposition, unless otherwise specified herein.

These terms may be defined with additional language in the remainingportions of the specification.

Detailed Description

Absorbent composites of this invention are useful in absorbent articles.An absorbent article of the present invention can have an absorbentcore, and can additionally include a topsheet, a backsheet, where theabsorbent core can be disposed between the topsheet and the backsheet.The absorbent core comprises an absorbent composite that includes thesuperabsorbent polymer composition of the present invention.

To gain a better understanding of the present invention, attention isdirected to FIG. 5 and FIG. 6 for exemplary purposes showing a trainingpant of the present invention. It is understood that the presentinvention is suitable for use with various other absorbent articles,including but not limited to other personal care absorbent articles,health/medical absorbent articles, household/industrial absorbentarticles, sports/construction absorbent articles, and the like, withoutdeparting from the scope of the present invention.

Various materials and methods for constructing training pants aredisclosed in PCT Patent Application No. WO 00/37009 published Jun. 29,2000 by A. Fletcher et al.; U.S. Pat. No. 4,940,464 to Van Gompel etal.; U.S. Pat. No. 5,766,389 to Brandon et al., and U.S. Pat. No.6,645,190 to Olson et al., all of which are incorporated herein byreference in a manner that is consistent herewith.

FIG. 5 illustrates a training pant in a partially fastened condition,and FIG. 6 illustrates a training pant in an opened and unfolded state.The training pant defines a longitudinal direction 48 that extends fromthe front of the training pant when worn to the back of the trainingpant. Perpendicular to the longitudinal direction 48 is a lateraldirection 49.

The pair of training pants defines a front region 22, a back region 24,and a crotch region 26 extending longitudinally between andinterconnecting the front and back regions. The pant also defines aninner surface adapted in use (e.g., positioned relative to the othercomponents of the pant) to be disposed toward the wearer, and an outersurface opposite the inner surface. The training pant has a pair oflaterally opposite side edges and a pair of longitudinally oppositewaist edges.

The illustrated pant 20 may include a chassis 32, a pair of laterallyopposite front side panels 34 extending laterally outward at the frontregion 22 and a pair of laterally opposite back side panels 134extending laterally outward at the back region 24.

The chassis 32 includes a backsheet 40 and a topsheet 42 that may bejoined to the backsheet 40 in a superimposed relation therewith byadhesives, ultrasonic bonds, thermal bonds or other conventionaltechniques. The chassis 32 further includes an absorbent core 44 forabsorbing fluid body exudates exuded by the wearer such as shown in FIG.6 disposed between the backsheet 40 and the topsheet 42. The chassis 32may further include a pair of containment flaps 46 secured to thetopsheet 42 or the absorbent core 44 for inhibiting the lateral flow ofbody exudates.

The backsheet 40, the topsheet 42 and the absorbent core 44 may be madefrom many different materials known to those skilled in the art. Any ofthe three layers, for instance, may be extensible and/or elasticallyextensible. Further, the stretch properties of each layer may vary inorder to control the overall stretch properties of the product.

The backsheet 40, for instance, may be breathable and/or may be fluidimpermeable. The backsheet 40 may be constructed of a single layer,multiple layers, laminates, spunbond fabrics, films, meltblown fabrics,elastic netting, microporous webs or bonded-carded-webs. The backsheet40, for instance, can be a single layer of a fluid impermeable material,or alternatively can be a multi-layered laminate structure in which atleast one of the layers is fluid impermeable.

The backsheet 40 can be biaxially extensible and optionally biaxiallyelastic. Elastic non-woven laminate webs that can be used as thebacksheet 40 include a non-woven material joined to one or moregatherable non-woven webs or films. Stretch Bonded Laminates (SBL) andNeck Bonded Laminates (NBL) are examples of elastomeric composites.

Examples of suitable nonwoven materials are spunbond-meltblown fabrics,spunbond-meltblown-spunbond fabrics, spunbond fabrics, or laminates ofsuch fabrics with films, or other nonwoven webs. Elastomeric materialsmay include cast or blown films, meltblown fabrics or spunbond fabricscomposed of polyethylene, polypropylene, or polyolefin elastomers, aswell as combinations thereof. The elastomeric materials may includePEBAX elastomer (available from AtoFina Chemicals, Inc., a businesshaving offices located in Philadelphia, Pa. U.S.A.), HYTREL elastomericpolyester (available from Invista, a business having offices located inWichita, Kans. U.S.A.), KRATON elastomer (available from KratonPolymers, a business having offices located in Houston, Tex., U.S.A.),or strands of LYCRA elastomer (available from Invista), or the like, aswell as combinations thereof. The backsheet 40 may include materialsthat have elastomeric properties through a mechanical process, printingprocess, heating process or chemical treatment. For example, suchmaterials may be apertured, creped, neck-stretched, heat activated,embossed, and micro-strained, and may be in the form of films, webs, andlaminates.

One example of a suitable material for a biaxially stretchable backsheet40 is a breathable elastic film/nonwoven laminate, such as described inU.S. Pat. No. 5,883,028, to Morman et al., incorporated herein byreference in a manner that is consistent herewith. Examples of materialshaving two-way stretchability and retractability are disclosed in U.S.Pat. No. 5,116,662 to Morman and U.S. Pat. No. 5,114,781 to Morman, eachof which is incorporated herein by reference in a manner that isconsistent herewith. These two patents describe composite elasticmaterials capable of stretching in at least two directions. Thematerials have at least one elastic sheet and at least one neckedmaterial, or reversibly necked material, joined to the elastic sheet atleast at three locations arranged in a nonlinear configuration, so thatthe necked, or reversibly necked, web is gathered between at least twoof those locations.

The topsheet 42 is suitably compliant, soft-feeling and non-irritatingto the wearer's skin. The topsheet 42 is also sufficiently liquidpermeable to permit liquid body exudates to readily penetrate throughits thickness to the absorbent core 44. A suitable topsheet 42 may bemanufactured from a wide selection of web materials, such as porousfoams, reticulated foams, apertured plastic films, woven and non-wovenwebs, or a combination of any such materials. For example, the topsheet42 may include a meltblown web, a spunbonded web, or a bonded-carded-webcomposed of natural fibers, synthetic fibers or combinations thereof.The topsheet 42 may be composed of a substantially hydrophobic material,and the hydrophobic material may optionally be treated with a surfactantor otherwise processed to impart a desired level of wettability andhydrophilicity.

The topsheet 42 may also be extensible and/or elastomericallyextensible. Suitable elastomeric materials for construction of thetopsheet 42 can include elastic strands, LYCRA elastics, cast or blownelastic films, nonwoven elastic webs, meltblown or spunbond elastomericfibrous webs, as well as combinations thereof. Examples of suitableelastomeric materials include KRATON elastomers, HYTREL elastomers,ESTANE elastomeric polyurethanes (available from Noveon, a businesshaving offices located in Cleveland, Ohio U.S.A.), or PEBAX elastomers.The topsheet 42 can also be made from extensible materials such as thosedescribed in U.S. Pat. No. 6,552,245 to Roessler et al. which isincorporated herein by reference in a manner that is consistentherewith. The topsheet 42 can also be made from biaxially stretchablematerials as described in U.S. Pat. No. 6,641,134 filed to Vukos et al.which is incorporated herein by reference in a manner that is consistentherewith.

The article 20 can optionally further include a surge management layer(not shown) which may be located adjacent the absorbent core 44 andattached to various components in the article 20 such as the absorbentcore 44 or the topsheet 42 by methods known in the art, such as by usingan adhesive. In general, a surge management layer helps to quicklyacquire and diffuse surges or gushes of liquid that may be rapidlyintroduced into the absorbent structure of the article. The surgemanagement layer can temporarily store the liquid prior to releasing itinto the storage or retention portions of the absorbent core 44.Examples of suitable surge management layers are described in U.S. Pat.No. 5,486,166 to Bishop et al.; U.S. Pat. No. 5,490,846 to Ellis et al.;and U.S. Pat. No. 5,820,973 to Dodge et al., all of which areincorporated herein by reference in a manner that is consistentherewith.

The article 20 can further comprise an absorbent core 44 which comprisesthe absorbent composite of the present invention. The absorbent core 44may have any of a number of shapes. For example, it may have a2-dimensional or 3-dimensional configuration, and may be rectangularshaped, triangular shaped, oval shaped, race-track shaped, I-shaped,generally hourglass shaped, T-shaped and the like. It is often suitablefor the absorbent core 44 to be narrower in the crotch portion 26 thanin the rear 24 or front 22 portion(s). The absorbent core 44 can beattached in an absorbent article, such as to the backsheet 40 and/or thetopsheet 42 for example, by bonding means known in the art, such asultrasonic, pressure, adhesive, aperturing, heat, sewing thread orstrand, autogenous or self-adhering, hook-and-loop, or any combinationthereof.

In some aspects, the absorbent core 44 can have a significant amount ofstretchability. For example, the absorbent core 44 can comprise a matrixof fibers which includes an operative amount of elastomeric polymerfibers. Other methods known in the art can include attachingsuperabsorbent material to a stretchable film, utilizing a nonwovensubstrate having cuts or slits in its structure, and the like.

The absorbent core 44 can be formed using methods known in the art.While not being limited to the specific method of manufacture, theabsorbent core can utilize a meltblown process and can optionally beformed on a coform line. Exemplary meltblown processes are described invarious patents and publications, including NRL Report 4364,“Manufacture of Super-Fine Organic Fibers” by V. A. Wendt, E. L. Booneand C. D. Fluharty; NRL Report 5265, “An Improved Device For theFormation of Super-Fine Thermoplastic Fibers” by K. D. Lawrence, R. T.Lukas and J. A. Young; and U.S. Pat. No. 3,849,241 to Butin et al. andU.S. Pat. No. 5,350,624 to Georger et al., all of which are incorporatedherein by reference in a manner that is consistent herewith.

To form “coform” materials, additional components are mixed with themeltblown fibers as the fibers are deposited onto a forming surface. Forexample, the absorbent composition of the present invention and fluff,such as wood pulp fibers, may be injected into the meltblown fiberstream so as to be entrapped and/or bonded to the meltblown fibers.Exemplary coform processes are described in U.S. Pat. No. 4,100,324 toAnderson et al.; U.S. Pat. No. 4,587,154 to Hotchkiss et al.; U.S. Pat.No. 4,604,313 to McFarland et al.; U.S. Pat. No. 4,655,757 to McFarlandet al.; U.S. Pat. No. 4,724,114 to McFarland et al.; U.S. Pat. No.4,100,324 to Anderson et al.; and U.K. Patent No. GB 2,151,272 to Mintoet al., all of which are incorporated herein by reference in a mannerthat is consistent herewith. Absorbent, elastomeric meltblown webscontaining high amounts of superabsorbent are described in U.S. Pat. No.6,362,389 to D. J. McDowall, and absorbent, elastomeric meltblown webscontaining high amounts of superabsorbent and low superabsorbentshakeout values are described in pending U.S. Publication No.2006/0004336 to X. Zhang et al., all of which are incorporated herein byreference in a manner that is consistent herewith.

One example of a method of forming an absorbent core 44 for use in thepresent invention is illustrated in FIG. 7. The dimensions of theapparatus in FIG. 7 are described herein by way of example. Other typesof apparatus having different dimensions and/or different structures mayalso be used to form the absorbent core 44. As shown in FIG. 7,elastomeric material 72 in the form of pellets can be fed through twopellet hoppers 74 into two single screw extruders 76 that each feed aspin pump 78. The elastomeric material 72 may be a multicomponentelastomer blend available under the trade designation VISTMAXX 2370 fromExxonMobil Chemical Company (a business having offices located inHouston, Tex., U.S.A.), as well as others mentioned herein. Each spinpump 78 feeds the elastomeric material 72 to a separate meltblown die80. Each meltblown die 80 may have 30 holes per inch (hpi). The dieangle may be adjusted anywhere between 0 and 70 degrees from horizontal,and is suitably set at about 45 degrees. The forming height may be at amaximum of about 16 inches (40.6 cm), but this restriction may differwith different equipment.

A chute 82 having a width of about 24 inches (61 cm) wide may bepositioned between the meltblown dies 80. The depth, or thickness, ofthe chute 82 may be adjustable in a range from about 0.5 to about 1.25inches (1.3 cm to 3.2 cm), or from about 0.75 to about 1.0 inch (1.9 cmto 2.5 cm). A picker 144 connects to the top of the chute 82. The picker144 is used to fiberize the pulp fibers 86. The picker 144 may belimited to processing low strength or debonded (treated) pulps, in whichcase the picker 144 may limit the illustrated method to a very smallrange of pulp types. In contrast to conventional hammermills that usehammers to impact the pulp fibers repeatedly, the picker 144 uses smallteeth to tear the pulp fibers 86 apart. Suitable pulp fibers 86 for usein the method illustrated in FIG. 7 include those mentioned herein, suchas NB480 (available from Weyerhaeuser Co., a business having officeslocated in Federal Way, Wash., U.S.A.).

At an end of the chute 82 opposite the picker 144 is a superabsorbentpolymer feeder 88. The feeder 88 pours the superabsorbent polymercomposition 90 of the present invention into a hole 92 in a pipe 94which then feeds into a blower fan 96. Past the blower fan 96 is alength of 4-inch (10-cm) diameter pipe 98 sufficient for developing afully developed turbulent flow at about 5,000 feet per minute, whichallows the superabsorbent polymer composition particles 90 to becomedistributed. The pipe 98 widens from a 4-inch (10 cm) diameter to the24-inch by 0.75-inch (61 cm by 1.9 cm) chute 82, at which point thesuperabsorbent polymer composition 90 mixes with the pulp fibers 86 andthe mixture falls straight down and gets mixed on either side at anapproximately 45-degree angle with the elastomeric material 72. Themixture of superabsorbent polymer composition 90, pulp fibers 86, andelastomeric material 72 falls onto a wire conveyor 100 moving from about14 to about 35 feet per minute. However, before hitting the wireconveyor 100, a spray boom 102 optionally sprays an aqueous surfactantmixture 104 in a mist through the mixture, thereby rendering theresulting absorbent core 44 wettable. The surfactant mixture 104 may bea 1:3 mixture of GLUCOPON 220 UP (available from Cognis Corporationhaving a place of business in Cincinnati, Ohio, U.S.A.) and AHCOVEL BaseN-62 (available from Uniqema, having a place of business in New Castle,Del., U.S.A.). An under wire vacuum 106 is positioned beneath theconveyor 100 to assist in forming the absorbent core 44.

In general, the absorbent core 44 is often a unitary structurecomprising a substantially uniform distribution of superabsorbentpolymer composition particles, fibers, and any other optional additives.However, referring to FIG. 8, in some aspects, the absorbent core 44 maybe further enhanced through structural modifications when combined withsuperabsorbent polymer composition of the present invention. Forexample, providing a layer 60 comprising substantially onlysuperabsorbent polymer composition particles of the present inventionsandwiched between layers 62 and 64 comprising substantially only flufffibers, such as NB480, or other natural or synthetic fibers can resultin an absorbent core having improved absorbent properties, such as fluidinsult intake rate, when compared to a structure comprising asubstantially uniform distribution of the superabsorbent polymercomposition and fluff fibers. Such layering can occur in the z-directionof the absorbent core and may optionally cover the entire x-y area.However, the layers 60, 62 and 64 need not be discreet from one another.For example, in some aspects, the z-directional middle portion 60 of theabsorbent core need only contain a higher superabsorbent polymercomposition percentage (e.g., at least about 10% by weight higher) thanthe top layer 62 and/or bottom layer 64 of the absorbent core.Desirably, the layers are present in the area of the absorbent core thatis within an insult target zone.

As referenced above, the absorbent core 44 includes absorbent material,such as the superabsorbent polymer composition of the present inventionand/or fluff. Additionally, the superabsorbent polymer composition canbe operatively contained within a matrix of fibers, such as polymericfibers. Accordingly, the absorbent core 44 can comprise a quantity ofthe superabsorbent polymer composition and/or fluff contained within amatrix of fibers. In some aspects, the amount of superabsorbent polymercomposition in the absorbent core 44 can be at least about 10% by weightof the core, such as at least about 30%, or at least about 60% by weightor at least about 90%, or between about 10% and about 99% by weight ofthe core, or between about 30% to about 90% by weight of the core, orbetween about 60% and about 95% by weight of the core to provideimproved benefits. Optionally, the amount of superabsorbent polymercomposition can be at least about 95% by weight of the core. In otheraspects, the absorbent core 44 can comprise about 35% or less by weightfluff, such as about 20% or less, or 10% or less by weight fluff.

It should be understood that the present invention is not restricted touse with the superabsorbent polymer composition and/or fluff. In someaspects, the absorbent core 44 may additionally or alternatively includematerials such as surfactants, ion exchange resin particles,moisturizers, emollients, perfumes, natural fibers, synthetic fibers,fluid modifiers, odor control additives, and combinations thereof.Alternatively, the absorbent core 44 can include a foam.

In order to function well, the absorbent core 44 can have certaindesired properties to provide improved performance as well as greatercomfort and confidence among the user. For instance, the absorbent core44 can have corresponding configurations of absorbent capacities,densities, basis weights and/or sizes which are selectively constructedand arranged to provide desired combinations of absorbency propertiessuch as liquid intake rate, absorbent capacity, liquid distribution orfit properties such as shape maintenance and aesthetics. Likewise, thecomponents can have desired wet to dry strength ratios, mean flow poresizes, permeabilities and elongation values.

In some aspects, absorbent core 44 can optionally include elastomericpolymer fibers. The elastomeric material of the polymer fibers mayinclude an olefin elastomer or a non-olefin elastomer, as desired. Forexample, the elastomeric fibers can include olefinic copolymers,polyethylene elastomers, polypropylene elastomers, polyester elastomers,polyisoprene, cross-linked polybutadiene, diblock, triblock, tetrablock,or other multi-block thermoplastic elastomeric and/or flexiblecopolymers such as block copolymers including hydrogenatedbutadiene-isoprene-butadiene block copolymers; stereoblockpolypropylenes; graft copolymers, including ethylene-propylene-dieneterpolymer or ethylene-propylene-diene monomer (EPDM) rubber,ethylene-propylene random copolymers (EPM), ethylene propylene rubbers(EPR), ethylene vinyl acetate (EVA), and ethylene-methyl acrylate (EMA);and styrenic block copolymers including diblock and triblock copolymerssuch as styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS),styrene-isoprene-butadiene-styrene (SIBS),styrene-ethylene/butylene-styrene (SEBS), orstyrene-ethylene/propylene-styrene (SEPS), which may be obtained fromKraton Inc. under the trade designation KRATON elastomeric resin or fromDexco, a division of ExxonMobil Chemical Company under the tradedesignation VECTOR (SIS and SBS polymers); blends of thermoplasticelastomers with dynamic vulcanized elastomer-thermoplastic blends;thermoplastic polyether ester elastomers; ionomeric thermoplasticelastomers; thermoplastic elastic polyurethanes, including thoseavailable from Invista Corporation under the trade name LYCRApolyurethane, and ESTANE available from Noveon, Inc., a business havingoffices located in Cleveland, Ohio, U.S.A.; thermoplastic elasticpolyamides, including polyether block amides available from AtoFinaChemicals, Inc. (a business having offices located in Philadelphia, Pa.,U.S.A.) under the trade name PEBAX; polyether block amide; thermoplasticelastic polyesters, including those available from E. I. Du Pont deNemours Co., under the trade name HYTREL, and ARNITEL from DSMEngineering Plastics (having a place of business located in Evansville,Ind., U.S.A.) and single-site or metallocene-catalyzed polyolefinshaving a density of less than about 0.89 grams/cubic centimeter,available from Dow Chemical Co. (having a place of business located inFreeport, Tex., U.S.A.) under the trade name AFFINITY; and combinationsthereof.

As used herein, a tri-block copolymer has an ABA structure where the Arepresents several repeat units of type A, and B represents severalrepeat units of type B. As mentioned above, several examples of styrenicblock copolymers are SBS, SIS, SIBS, SEBS and SEPS. In these copolymersthe A blocks are polystyrene and the B blocks are a rubbery component.Generally, these triblock copolymers have molecular weights that canvary from the low thousands to hundreds of thousands, and the styrenecontent can range from 5% to 75% based on the weight of the triblockcopolymer. A diblock copolymer is similar to the triblock, but is of anAB structure. Suitable diblocks include styrene-isoprene diblocks, whichhave a molecular weight of approximately one-half of the triblockmolecular weight having the same ratio of A blocks to B blocks.

In desired arrangements, the polymer fibers can include at least onematerial selected from the group consisting of styrenic blockcopolymers, elastic polyolefin polymers and co-polymers and EVA/EMA typepolymers.

In some particular arrangements, for example, the elastomeric materialof the polymer fibers can include various commercial grades of lowcrystallinity, lower molecular weight metallocene polyolefins, availablefrom ExxonMobil Chemical Company (a company having offices located inHouston, Tex., U.S.A.) under the VISTAMAXX trade designation. SomeVISTAMAXX materials are believed to be metallocene propylene ethyleneco-polymer. For example, in one aspect the elastomeric polymer can beVISTAMAXX PLTD 2210. In other aspects, the elastomeric polymer can beVISTAMAXX PLTD 1778. In a particular aspect, the elastomeric polymer isVISTAMAXX 2370. Another optional elastomeric polymer is KRATON blend G2755 from Kraton Inc. The KRATON material is believed to be a blend ofstyrene ethylene-butylene styrene polymer, ethylene waxes and tackifyingresins.

In some aspects, the elastomeric polymer fibers can be produced from apolymer material having a selected melt flow rate (MFR). In a particularaspect, the MFR can be up to a maximum of about 300. Alternatively, theMFR can be up to about 230 or 250. In another aspect, the MFR can be aminimum of not less than about 9, or not less than 20. The MFR canalternatively be not less than about 50 to provide desired performance.The described melt flow rate has the units of grams flow per 10 minutes(g/10 min). The parameter of melt flow rate is well known, and can bedetermined by conventional techniques, such as by employing test ASTM D1238 70 “extrusion plastometer” Standard Condition “L” at 230° C. and2.16 kg applied force.

As referenced above, the polymer fibers of the absorbent core 44 caninclude an amount of a surfactant. The surfactant can be combined withthe polymer fibers of the absorbent core in any operative manner.Various techniques for combining the surfactant are conventional andwell known to persons skilled in the art. For example, the surfactantmay be compounded with the polymer employed to form a meltblown fiberstructure. In a particular feature, the surfactant may be configured tooperatively migrate or segregate to the outer surface of the fibers uponthe cooling of the fibers. Alternatively, the surfactant may be appliedto or otherwise combined with the polymer fibers after the fibers havebeen formed.

The polymer fibers can include an operative amount of surfactant, basedon the total weight of the fibers and surfactant. In some aspects, thepolymer fibers can include at least a minimum of about 0.1% by weightsurfactant, as determined by water extraction. The amount of surfactantcan alternatively be at least about 0.15% by weight, and can optionallybe at least about 0.2% by weight to provide desired benefits. In otheraspects, the amount of surfactant can be generally not more than amaximum of about 2% by weight, such as not more than about 1% by weight,or not more than about 0.5% by weight to provide improved performance.

If the amount of surfactant is outside the desired ranges, variousdisadvantages can occur. For example, an excessively low amount ofsurfactant may not allow fibers, such as hydrophobic meltblown fibers,to wet with the absorbed fluid. In contrast, an excessively high amountof surfactant may allow the surfactant to wash off from the fibers andundesirably interfere with the ability of the absorbent core totransport fluid, or may adversely affect the attachment strength of theabsorbent core to the absorbent article. Where the surfactant iscompounded or otherwise internally added to the polymer fibers, anexcessively high level of surfactant can create conditions that causepoor formation of the polymer fibers and interfiber bonds.

In some configurations, the surfactant can include at least one materialselected from the group that includes polyethylene glycol estercondensates and alkyl glycoside surfactants. For example, the surfactantcan be a GLUCOPON surfactant, available from Cognis Corporation, whichcan be composed of 40% water, and 60% d-glucose, decyl, octyl ethers andoligomerics.

In other aspects of the invention, the surfactant can be in the form ofa sprayed-on surfactant comprising a water/surfactant solution whichincludes 16 liters of hot water (about 45° C. to 50° C.) mixed with 0.20kg of GLUCOPON 220 UP surfactant available from Cognis Corporation and0.36 kg of AHCHOVEL Base N-62 surfactant available from Uniqema. Whenemploying a sprayed-on surfactant, a relatively lower amount ofsprayed-on surfactant may be desirable to provide the desiredcontainment of the superabsorbent polymer particles. Excessive amountsof the fluid surfactant may hinder the desired attachment of thesuperabsorbent polymer particles to the molten, elastomeric meltblownfibers, for example.

An example of an internal surfactant or wetting agent that can becompounded with the elastomeric fiber polymer can include a MAPEG DO 400PEG (polyethylene glycol) ester, available from BASF (a business havingoffices located in Freeport, Tex., U.S.A.). Other internal surfactantscan include a polyether, a fatty acid ester, a soap or the like, as wellas combinations thereof.

In some aspects, the absorbent core 44 can include fluff, such ascellulosic fibers. Such cellulosic fibers may include, but are notlimited to, chemical wood pulps such as sulfite and sulfate (sometimescalled Kraft) pulps, as well as mechanical pulps such as ground wood,thermomechanical pulp and chemithermomechanical pulp. More particularly,the pulp fibers may include cotton, other typical wood pulps, celluloseacetate, debonded chemical wood pulp, and combinations thereof. Pulpsderived from both deciduous and coniferous trees can be used.Additionally, the cellulosic fibers may include such hydrophilicmaterials as natural plant fibers, milkweed floss, cotton fibers,microcrystalline cellulose, microfibrillated cellulose, or any of thesematerials in combination with wood pulp fibers. Suitable cellulosicfluff fibers can include, for example, NB480 (available fromWeyerhaeuser Co.); NB416, a bleached southern softwood Kraft pulp(available from Weyerhaeuser Co.); COOSABSORB S, a bleached southernsoftwood Kraft pulp (available from Bowater Inc., a business havingoffices located in Greenville, S.C. U.S.A.).; SULPHATATE HJ, achemically modified hardwood pulp (available from Rayonier Inc., abusiness having offices located in Jesup, Ga., U.S.A.); NF 405, achemically treated bleached southern softwood Kraft pulp (available fromWeyerhaeuser Co.); and CR 1654, a mixed bleached southern softwood andhardwood Kraft pulp (available from Bowater Inc.)

The absorbent core 44 also includes a desired amount of thesuperabsorbent polymer composition of the present invention. In general,superabsorbent polymers (SAPs) may be rendered water insoluble, butwater swellable. These internally crosslinked polymers can be at leastpartially neutralized.

SAPs are manufactured by known polymerization techniques, such as bypolymerization in aqueous solution by gel polymerization. The result ofthis polymerization process is a polymer with superabsorbent properties,which can then be reduced in size to small particles by mechanicalforces and dried using drying procedures and apparatus known in the art.The drying process can be followed by pulverization of the resultingparticles to the desired particle size. In general, particles too smallin size swell after absorbing a fluid and can block the absorption offurther fluid, while particles too large in size have a reduced surfacearea which can decrease the rate of absorption.

The superabsorbent polymer compositions of the present invention can besubstantially homogeneously mixed with a hydrophilic composite fibermatrix or can be nonuniformly mixed. The fiber and superabsorbentparticles can also be selectively placed into desired regions of theabsorbent core 44, such as in the target zone for example, to bettercontain and absorb body exudates. The concentration of thesuperabsorbent particles can also vary through the thickness of theabsorbent core 44. Alternatively, absorbent core 44 can include alaminate of fibrous webs and superabsorbent material or other suitablemeans of maintaining a superabsorbent material in a localized area.

In one aspect of the invention, the superabsorbent polymer compositionis capable of swelling and absorbing fluid at an initial absorbentcapacity and, when a triggering mechanism is relased, swelling andabsorbing fluid at a second capacity which is at least about 25% greaterthan the first absorbent capacity, as measured by the ModifiedCentrifuge Retention Capacity (mCRC) Test described above, thusproviding a stepped capacity. As used herein, “swelling” refers to thegrowth in mass of the superabsorbent polymer composition that occurswhile fluids are being absorbed by the superabsorbent material. Forswelling to occur in superabsorbent polymer compositions, fluids must beabsorbed. Thus, it is understood that swelling of the superabsorbentmaterial also means that the superabsorbent material is absorbing fluid.

The superabsorbent polymer compositions of the present invention arecapable of swelling and absorbing additional fluids after a triggeringmechanism is released. In one aspect, triggering mechanisms functionafter the superabsorbent material is saturated, or substantiallysaturated, with absorbed liquid. The triggering mechanism can cause thesuperabsorbent material to swell and absorb additional amounts of fluidsas compared to the same superabsorbent material prior to release of thatparticular triggering mechanism.

Triggering mechanisms useful in this invention include, withoutlimitation, materials which react to thermal, chemical, mechanical,electrical, magnetic, or radiation energy. Triggering mechanisms mayalso include a combination of these mechanisms or other mechanisms whichcan cause the superabsorbent polymer compositions to absorb additionalfluids.

In some aspects of the present invention, an absorbent compositecomprises a water-insoluble fibrous matrix, a superabsorbent polymercomposition, and at least one triggering mechanism. In some aspects, atriggering mechanism can be incorporated directly into thesuperabsorbent polymer composition. In other aspects, a triggeringmechanism can be located on a surface of the superabsorbent polymercomposition. In yet other aspects, a triggering mechanism can be locatedwithin the absorbent composite fibrous matrix, but not necessarily indirect contact with the superabsorbent polymer composition. In stillother aspects, triggering mechanisms may be incorporated into theabsorbent composite through a combination of the techniques describedabove. It is understood that other variations of incorporating atriggering mechanism into the present invention are also suitable, andthe techniques described above are provided for exemplary purposes onlyand should not be considered as limiting.

In addition, triggering mechanisms can be applied by means of blending,encapsulation, coating, printing, laminating, strategically blendingand/or placing in a specific pocket of the composite, as well ascombinations of these, or other means. A particular triggering mechanismmay have time delayed effects, and only start to function when sucheffects are eliminated. One non-limiting example is an encapsulatedtriggering mechanism. The triggering materials may be usedsynergistically with or without any time-controlled release or delayfunctions.

In some aspects, the triggering mechanism can be located throughout theentire absorbent composite. In other aspects, the triggering mechanismcan be located in a predetermined region of the absorbent composite. Thepredetermined region can be the target zone of the absorbent composite.In some aspects, around the target zone can optionally be a secondsuperabsorbent material not affected by the triggering mechanism. Thepredetermined region of the absorbent composite can also be locatedoutside of the target zone or overlapping both the target zone and anarea outside the target zone.

In some aspects, an absorbent composite of the present inventioncomprises a first triggering mechanism. By way of example, the firsttriggering mechanism can have a suitable first release time of about 5to 60 minutes. For example, in the case of an encapsulated triggeringmechanism, the release time is the time required to dissolve orsubstantially dissolve the material which encapsulates the triggeringmechanism, thereby allowing the triggering mechanism to effect thesuperabsorbent polymer composition. Dissolution of the triggeringmechanism can be initiated through various means including, but notlimited to, a fluid insult of the absorbent composite. The initialabsorbent capacity of the superabsorbent material before the firsttriggering mechanism is released is suitably at least about 5 gramsfluid per gram of superabsorbent material, such as at least about 10grams fluid per gram of superabsorbent material, or at least about 12grams fluid per gram of superabsorbent material, as measured by the mCRCTest. After the triggering mechanism has been released, thesuperabsorbent material has a second absorbent capacity that is at leastabout 25% greater than the initial absorbent capacity, such as at leastabout 30% greater or at least about 35% greater than the initialabsorbent capacity.

In other aspects of the present invention, the absorbent composite cancontain multiple triggering mechanisms with varying release times torelease one triggering mechanism after another to provide an absorbentcomposite having a multiple stepped capacity (i.e., each consecutiveabsorbent capacity is at least about 25% higher than the previousabsorbent capacity, as measured by the mCRC Test). For example, a secondtriggering mechanism can be used in conjunction with the firsttriggering mechanism, such as described above. The second triggeringmechanism will desirably have a release time that is greater than thefirst triggering mechanism. By way of example, a suitable release timefor the second triggering mechanism can be about 10 to 120 minutes fromthe initial fluid insult and at least 5 minutes greater than that of thefirst triggering mechanism release time. Release of the secondencapsulated triggering mechanism will result in a third absorbentcapacity that is at least about 25% greater than the second absorbentcapacity obtained after release of the first triggering mechanism, suchas at least about 30% greater or at least about 35% greater than thesecond absorbent capacity.

In further aspects of the present invention, a third triggeringmechanism can be used to provide yet another stepped capacity. The thirdtriggering mechanism will desirably have a release time that is greaterthan the second triggering mechanism. By way of example, a suitablethird release time for the third triggering mechanism can be about 15 to180 minutes from the initial fluid insult and at least 5 minutes greaterthan the second release time. Release of the third triggering mechanismwill result in a fourth absorbent capacity that is at least about 25%greater than the third absorbent capacity obtained after release of thesecond triggering mechanism, such as at least about 30% greater or atleast about 35% greater than the third absorbent capacity.

In further aspects of the present invention, a fourth triggeringmechanism can be used to provide yet another stepped capacity. Thefourth triggering mechanism will desirably have a release time greaterthan that of the third triggering mechanism. By way of example, asuitable fourth release time for the fourth triggering mechanism can beabout 20 to 240 minutes and at least 5 minutes greater than the thirdrelease time. Release of the fourth encapsulated triggering mechanismwill result in a fifth absorbent capacity that is at least about 25%greater than the fourth absorbent capacity obtained after release of thethird triggering mechanism, such as at least about 30% greater or atleast about 35% greater than the fourth absorbent capacity.

In some aspects of the present invention, superabsorbent materials, suchas those having a low absorbent capacity, for example by lowneutralization levels, can be triggered to swell to a higher absorbentcapacity (i.e., a “step capacity” change) by a change in pH of thesuperabsorbent environment. For example, superabsorbent polymercompositions can be triggered to swell by the addition of a basic or anacidic compound or solution. In general, if the superabsorbent materialis an anionic superabsorbent material, then the triggering mechanismwill include a base. If the superabsorbent material is a cationicsuperabsorbent material, then the triggering mechanism will include anacid. In some aspects, a base or acid in the form of a solid may bedesirable.

In some aspects, a weakly basic or weakly acidic compound may bedesirable. Using weaker acids and/or bases, such as citric acid orbaking soda in the absorbent composite can be safer for the user thanstronger acids and/or bases such as hydrochloric acid or sodiumhydroxide. In one aspect of the present invention, the desirable pHrange for an absorbent composite comprising an acid triggering mechanismis a pH that is less than the original pH value of the superabsorbentmaterial, such as about 4 to 7 when a weak acid is used, such as citricacid for example. In another aspect of the present invention, thedesired pH range for an absorbent composite comprising a base triggeringmechanism is a pH that is greater than the original pH value of thesuperabsorbent material, such as when the superabsorbent material is at70% neutralization.

In some aspects, when an acid or base is used as the triggeringmechanism, it may be desirable to blend the triggering mechanismdirectly into the superabsorbent material. In other aspects, it may bedesirable to refrain from directly blending the acid or base into thesuperabsorbent material. In order to activate a triggering mechanismwith a delayed effect at various lengths of time, the acid or base maybe shielded from direct or immediate contact with bodily fluid.Encapsulation, for example, of the acid or base with certain chemicalcoatings with different thickness and dissolution kinetics can helpachieve the desired time-delayed effect.

In other aspects of the present invention, the superabsorbent polymercomposition can be triggered to swell by a triggering mechanism whicheffects a change in ionic strength after release. For example, sodiumchloride in solid form can be included in the absorbent composite, whichmay or may not be incorporated into the superabsorbent material, andwhich results in a high ionic strength solution, such as 8% by weightsodium chloride, upon an initial fluid insult. The salt poisoning effectwhich results will limit the absorbent capacity of the superabsorbentmaterial to a desired level. When a subsequent insult of fluid occurswhich has a lower ionic strength solution, such as aqueous 0.9% sodiumchloride, the absorbent capacity will increase to a new, higher limit.This stepped capacity increase can continue until the ionic strength ofthe superabsorbent environment is equal to, or less than, the ionicstrength of the insulting fluid.

In some aspects, superabsorbent materials capable of stepped capacityswelling according to the present invention can be distributedthroughout the absorbent composite. In other aspects, the superabsorbentpolymer compositions can be localized to predetermined areas of anabsorbent composite. For example, FIG. 9 shows an absorbent article 710having an absorbent core 725 comprising an absorbent composite accordingto one aspect of the present invention. Absorbent core 725 can includethe superabsorbent polymer composition of the present invention locatedin a target zone region 728. An optional second superabsorbent materialcan be placed outside the target zone region 728 in outside regions 726,727. The superabsorbent polymer composition of the present inventionthat is located in the target zone region 728 has the ability to swellrelatively quickly (compared to a conventional SAP) once a triggeringmechanism is released, but will have a limited absorbent capacity. Fluidfrom each fluid insult that cannot be absorbed by the superabsorbentmaterial of the present invention located in the target zone region 728will be distributed and absorbed by the superabsorbent polymercomposition in the outside regions 726, 727. The absorbent capacity ofthe superabsorbent polymer composition in the target zone region 728 canthen be increased by release of another triggering mechanism such thatadditional fluid insulted into the target zone will quickly swell thesuperabsorbent material to a higher absorbent capacity limit, and theexcess fluid will once again distribute into the outside regions 726,727. Each limited absorbent capacity of the stepped capacitysuperabsorbent polymer composition results in lower overall swellingthickness in the target zone when compared to composites utilizingconventional SAPs, because excess fluid in the present invention isdistributed away from the target zone region 728. The result is anabsorbent composite that provides greater comfort and confidence to theuser.

Superabsorbent materials useful in this invention can initially absorb(i.e., prior to release of a first triggering mechanism) at least about5 grams of saline (i.e., 0.9 wt % aqueous sodium chloride solution) pergram of superabsorbent, such as at least about 10 grams of saline pergram of superabsorbent, or 12 grams of saline per gram ofsuperabsorbent, as measured by the mCRC Test. Stepped capacitysuperabsorbent materials useful in this invention can result in anabsorbent capacity that is at least about 25% greater after release of atriggering mechanism as compared to the same superabsorbent materialprior to release of the triggering mechanism. In some aspects, thesuperabsorbent polymer compositions of the present invention have aswelling rate that is at least about 20% greater than the swelling rateof conventional SAPs, such as at least about 50% greater, or 75%greater, or 100% greater than the swelling rate of conventional SAPs, asmeasured by the Swelling Rate Test.

The superabsorbent polymer compositions according to the invention canbe employed in many products including sanitary towels, diapers, orwound coverings, and they have the property that they rapidly absorblarge amounts of menstrual blood, urine, or other body fluids, forexample. Since the superabsorbent materials according to the inventionretain the absorbed liquids even under pressure and are also capable ofdistributing further liquid within the construction in the swollenstate, they are more desirably employed in higher concentrations, withrespect to other absorbent core components, such as fluff, when comparedto conventional current superabsorbent compositions. They are alsosuitable for use as a homogeneous superabsorber layer without fluffcontent within an absorbent article construction, as a result of whichparticularly thin articles are possible.

The preparation of laminates in the broadest sense, and of extruded andcoextruded, wet- and dry-bonded, as well as subsequently bondedstructures, are possible as further preparation processes. A combinationof these possible processes with one another is also possible.

In addition to the articles described above, the superabsorbent polymercompositions according to the invention may also be employed inabsorbent articles that are suitable for further uses. In particular,the superabsorbent polymer compositions of this invention can be used inpersonal care absorbent articles, health/medical absorbent articles,household/industrial absorbent articles, sports/construction absorbentarticles, and the like.

In addition to the absorbent article described above, the presentinvention may be exemplified as an absorbent bandage. Attention isdirected to FIGS. 10A and 10B, which show a possible configuration for abandage of the present invention. FIG. 10A shows a cross-section view ofthe absorbent bandage with optional layers described below. FIG. 10Bshows a perspective view of the bandage of the present invention withsome of the optional or removable layers not being shown. The absorbentbandage 150 has a strip 151 of material having a body-facing side 159and a second side 158 which is opposite the body-facing side. The stripis essentially a backsheet and is desirably prepared from the samematerials described above for the backsheet. In addition, the strip maybe an apertured material, such as an apertured film, or material whichis otherwise gas permeable, such as a gas permeable film. The strip 151supports an absorbent core 152 comprising the superabsorbent polymercomposition of the present invention which is attached to thebody-facing side 159 of the strip. In addition, an absorbent protectivelayer 153 may be applied to the absorbent core 152 and can becoextensive with the strip 151.

The absorbent bandage 150 of the present invention may also have apressure sensitive adhesive 154 applied to the body-facing side 159 ofthe strip 151. Any pressure sensitive adhesive may be used, providedthat the pressure sensitive adhesive does not irritate the skin of theuser. Suitably, the pressure sensitive adhesive is a conventionalpressure sensitive adhesive which is currently used on similarconventional bandages. This pressure sensitive adhesive is desirably notplaced on the absorbent core 152 or on the absorbent protective layer153 in the area of the absorbent core 152. If the absorbent protectivelayer is coextensive with the strip 151, then the adhesive may beapplied to areas of the absorbent protective layer 153 where theabsorbent core 152 is not located. By having the pressure sensitiveadhesive on the strip 151, the bandage is allowed to be secured to theskin of a user in need of the bandage. To protect the pressure sensitiveadhesive and the absorbent, a release strip 155 can be placed on thebody-facing side 159 of the bandage. The release liner may be removablysecured to the article attachment adhesive and serves to preventpremature contamination of the adhesive before the absorbent article issecured to, for example, the skin. The release liner may be placed onthe body-facing side of the bandage in a single piece (not shown) or inmultiple pieces, as is shown in FIG. 10A.

In another aspect of the present invention, the absorbent core of thebandage may be placed between a folded strip. If this method is used toform the bandage, the strip is suitably fluid permeable.

Absorbent furniture and/or bed pads or liners are also included withinthe present invention. As is shown in FIG. 11, a furniture or bed pad orliner 160 (hereinafter referred to as a “pad”) is shown in perspective.The pad 160 has a fluid impermeable backsheet 161 having afurniture-facing side or surface 168 and an upward facing side orsurface 169 which is opposite the furniture-facing side or surface 168.The fluid impermeable backsheet 161 supports the absorbent core 162which comprises the superabsorbent polymer composition of the presentinvention, and which is attached to the upward facing side 169 of thefluid impermeable backsheet. In addition, an optional absorbentprotective layer 163 may be applied to the absorbent core. The optionalsubstrate layer of the absorbent core can be the fluid impermeable layer161 or the absorbent protective layer 163 of the pad.

To hold the pad in place, the furniture-facing side 168 of the pad maycontain a pressure sensitive adhesive, a high friction coating or othersuitable material which will aid in keeping the pad in place during use.The pad of the present invention can be used in a wide variety ofapplications including placement on chairs, sofas, beds, car seats andthe like to absorb any fluid which may come into contact with the pad.

Sports or construction accessories, such as an absorbent headband forabsorbing perspiration or drying off equipment are also included withinthe present invention. As is shown in FIG. 12, an absorbent sweatband170 is shown in perspective. The sweatband 170 has an absorbent core 180disposed between an optional topsheet 174 and/or an optional fluidimpervious backsheet 176. The absorbent core 180 comprises thesuperabsorbent polymer composition of the present invention, and in someaspects can include an optional additional region 178 (such as adistribution layer), if desired. The sweatband can be useful tointercept perspiration prior to contact with the hands or eyes. VELCROor other fastening device 182 can be used to facilitate adjustment orcomfort.

The present invention may be better understood with reference to thefollowing examples.

EXAMPLES

Unless otherwise indicated, the conventional superabsorbent materialused in the Examples below was HYSORB 8850AD, available from BASF(having a place of business in Freeport, Tex., U.S.A.) and the flufffiber used was COOSABSORB S, a bleached southern softwood Kraft pulpavailable from Bowater Inc., (having a place of business located inGreenville, S.C. U.S.A.).

Example 1

A first series of computer simulations using finite element analysis wasrun to compare the fluid intake and fluid distribution of an absorbentsystem of the present invention with conventional absorbent systems. Anexemplary absorbent system, in the form of a pad, can be seen in FIG.13, shown generally as 810. A Comparative Example 1 was produced as acontrol, and had an absorbent system design that included “conventional”superabsorbent material. The conventional SAP had the followingproperties:

-   -   Mean Particle Size=400 um;    -   SAP Diffusion Coefficient=2×10⁻⁶ cm²/sec; and    -   SAP mCRC=30 g/g.

In comparison, Example 1, which represents absorbent systems comprisingthe superabsorbent polymer compositions of the present invention, hadthe following properties, which result in stepped capacity behavior:

-   -   Mean Particle Size=400 um;    -   SAP Diffusion Coefficient=6×10⁻⁶ cm²/sec;    -   For 1^(st) Insult and Hold Time: mCRC=8 g/g;    -   For 2^(nd) Insult and Hold Time: mCRC=15 g/g;    -   For 3^(rd) Insult and Hold Time: mCRC=21 g/g.

Additional input parameters of this first series of simulations wereheld constant for both absorbent systems, and include:

-   -   Three 70 ml fluid insults, followed by 4, 5, and 6 minute Hold        times (i.e., the amount of time between or after each fluid        insult), respectively.    -   Amount of superabsorbent material in the absorbent system=65 wt        %    -   Density of the pad=0.24 g/cc    -   Surge material basis weight=76 gsm    -   Liquid Insult region=21.5 cm², located 11.4 cm from front edge        830 of pad 810 (FIG. 13)    -   Absorbent system was tested while in a prone position    -   Pad shape 840 (FIG. 13)

Results of this first series of computer simulations are presented inTable 1 below, which demonstrate the time to intake each of the three 70ml insults.

TABLE 1 1^(st) Intake Time 2^(nd) Intake Time 3^(rd) Intake Time System(sec) (sec) (sec) Comparative 50 85 131 Example 1 Example 1 58 90 101

The distribution behavior of the absorbent systems from this firstseries of simulations can also be characterized by the saturation levelat the back 820 of the pad 810 at the end of each hold time period, asseen in Table 2 below and in FIG. 13:

TABLE 2 1^(st) Hold Back 2^(nd) Hold Back 3^(rd) Hold Back SaturationSaturation Saturation System (g/cm²) (g/cm²) (g/cm²) Comparative 0.02540.0808 0.165 Example 1 Example 1 0.0770 0.209 0.386

As can be seen from Table 1 and Table 2 above, the absorbent compositecontaining a stepped capacity superabsorbent shows generally similarintake properties as the conventional absorbent systems, but havesubstantially improved fluid distribution profiles.

Example 2

A second series of computer simulations using finite element analysiswas run to determine the impact of changes in the characteristics of thestepped capacity behavior on the fluid intake and fluid distribution ofabsorbent systems. An exemplary absorbent system, in the form of a pad,can be seen in FIG. 13, shown generally as 810. Example 2 was anabsorbent system design which included superabsorbent polymercomposition of the present invention having stepped capacity behavior.Comparative Example 2 was an absorbent system design which includedconventional superabsorbent material. The conventional superabsorbentmaterial system had the following properties:

-   -   Mean Particle Size=400 um    -   SAP Diffusion Coefficient=2×10⁻⁶ cm²/sec    -   SAP mCRC=30 g/g

This simulation was a designed experiment which systematically variesthe swelling rate and the 1^(st), 2^(nd), and 3^(rd) step capacities ofthe superabsorbent. The eight conditions simulated as part of thisdesigned experiment are list in Table 3 below:

TABLE 3 SAP mCRC SAP Diffusion Coefficient [1^(st), 2^(nd), 3^(rd)]Example (cm²/sec) (g/g) 2-1 4 × 10⁻⁶  6, 10, 20 2-2 4 × 10⁻⁶ 12, 20, 202-3 4 × 10⁻⁶ 12, 10, 30 2-4 4 × 10⁻⁶  6, 20, 30 2-5 8 × 10⁻⁶ 12, 10, 202-6 8 × 10⁻⁶  6, 20, 20 2-7 8 × 10⁻⁶  6, 10, 30 2-8 8 × 10⁻⁶ 12, 20, 30

Additional input parameters of this second series of simulations wereheld constant for both absorbent systems, and include:

-   -   Three 70 ml fluid insults, followed by 4, 5, and 6 minute Hold        times (i.e., the amount of time between or after each fluid        insult), respectively    -   Amount of superabsorbent material in the absorbent system=65 wt        %    -   Density of the pad=0.24 g/cc    -   Surge material basis weight=76 gsm    -   Liquid insult region=21.5 cm², located 11.4 cm from front edge        830 of pad 810 (FIG. 13)    -   Absorbent system was tested while in a prone position    -   Pad Shape 840 (FIG. 13)

Results of this second series of computer simulations are presented inTable 4 below, which demonstrates the intake rate after each of thethree 70 cc insults:

TABLE 4 1^(st) Intake Rate 2^(nd) Intake Rate 3^(rd) Intake Rate System(g/sec) (g/sec) (g/sec) Comparative 1.4 0.82 0.53 Example 2 Example 2-10.69 0.16 0.40 Example 2-2 1.33 0.88 0.27 Example 2-3 1.33 0.10 0.71Example 2-4 0.69 0.93 0.87 Example 2-5 1.73 0.11 0.58 Example 2-6 0.891.43 0.37 Example 2-7 0.89 0.23 1.15 Example 2-8 1.73 1.17 1.06

Changes to the behavior of the stepped capacity superabsorbent also havean effect on fluid distribution. The distribution of fluid through theabsorbent system can be characterized by the wet thickness in the targetzone area at the end of each hold period. A lower wet thickness in thetarget zone area results as more fluid being distributed throughout theabsorbent system. The wet thickness of the absorbent systems describedabove can be seen in Table 5 below.

TABLE 5 1^(st) Hold Time 2^(nd) Hold Time 3^(rd) Hold Time Wet WetThickness Wet Thickness Thickness System (cm) (cm) (cm) Comparative 0.510.76 0.95 Example 2 Example 2-1 0.38 0.49 0.76 Example 2-2 0.48 0.700.76 Example 2-3 0.48 0.49 0.87 Example 2-4 0.38 0.67 0.91 Example 2-50.50 0.48 0.76 Example 2-6 0.38 0.68 0.75 Example 2-7 0.36 0.47 0.89Example 2-8 0.50 0.73 0.97

As can be seen, certain combinations of SAP capacity and diffusioncoefficient at different stages can lead to maintaining liquid intakeperformance of commercial products, yet providing substantialdistribution improvement (as seen by a decrease in wet thickness in thetarget location).

Further, the intake and thickness results illustrated in Tables 4 and 5above, can be analyzed using known statistical methods to determinecombinations of stepped capacity superabsorbent behavior that can leadto even more desirable intake and thickness results. This statisticalanalysis led to another simulation condition with the superabsorbentproperties listed in Table 6 below. All other simulation parameters wereheld constant as described above.

TABLE 6 SAP mCRC SAP Diffusion Coefficient [1^(st), 2^(nd), 3^(rd)]System (cm²/sec) (g/g) Example 7 × 10⁻⁶ 9, 16, 20 2-9

Results of the computer simulation using the properties from Table 6 arepresented in Table 7 and Table 8 below, which demonstrates the intakerate for each of the three 70 ml insults, along with the wet thicknessin the target area.

TABLE 7 1^(st) Intake Rate 2^(nd) Intake Rate 3^(rd) Intake Rate System(g/sec) (g/sec) (g/sec) Example 2-9 1.36 0.88 0.66

It can be seen from Table 7 that composites of the present invention(i.e., comprising a stepped capacity superabsorbent polymer composition)result in longer wetted length and longer wetted area per gram of liquidloading. This demonstrates that the invention results in better liquidwicking/distribution when compared to absorbents having conventionalSAP.

TABLE 8 1^(st) Hold Wet 2^(nd) Hold Wet 3^(rd) Hold Wet ThicknessThickness Thickness System (cm) (cm) (cm) Example 2-9 0.45 0.65 0.83

As can be seen from Tables 7 and 8, the conditions simulated in Example2-9 lead to Intake Rates similar to the comparative example, however thefluid distribution is improved which results in the wet thickness at thetarget zone to be substantially less than the control.

Example 3

In this example, stepped capacity behavior was demonstrated bycontrolling the salt concentration of an insult liquid used in eachprogressive insult. Three liquid insults (each totaling 70 ml with 15minute intervals between each insult) were each added to an absorbentcomposite containing 60 wt % superabsorbent polymer composition of thepresent invention and the remainder fluff pulp (Example 3). For purposesof this example, the first insulting liquid was a solution of 8.0 wt %aqueous sodium chloride. The second and third insults were of a liquidsolution of 0.9% aqueous sodium chloride. A comparative example(Comparative Example 3) was also tested as a control using 0.9% sodiumchloride for all insults and represents an absorbent composite havingconventional superabsorbent material. Each composite was placed in ahorizontal position. The time for each liquid insult to enter the pad,the fluid distribution following a 15 minute hold time after eachinsult, and the thickness of the pad at the insult point after each holdtime were measured. The results can be seen in Table 9 below.

TABLE 9 1^(st) 2^(nd) 3^(rd) Intake Intake Intake 1^(st) Intake 2^(nd)Intake 3^(rd) Intake Rate Rate Rate Thickness Thickness Thickness Code(g/sec) (g/sec) (g/sec) (mm) (mm) (mm) Com- 2.28 2.25 2.22 10.4 12.012.7 parative Exam- ple 3 Exam- 1.97 2.09 1.11 6.5 9.6 11.4 ple 3

It can be seen from Table 9 that the intake rate for the absorbentcomposite of the present invention is generally similar to the intakerate of an absorbent composite having a conventional superabsorbentmaterial. However, the thickness of the absorbent composite of thepresent invention is less than that of the comparative example. Thisindicates improved fluid distribution by the present invention, as wellas greater comfort and fit for the user.

In addition, FIGS. 14-16 show a graphical demonstration of the fluiddistribution obtained in the examples after each insult, as measuredusing the Fluid Distribution Test described above. It can be seen thatan absorbent composite of the present invention exhibits an improvedfluid distribution when compared to an absorbent composite havingconventional superabsorbent material.

Example 4

Static Mannequin testing, as described in the Mannequin Test Procedureabove, was performed using absorbent articles in the form of a diaper.Each absorbent article of the present invention had a conventional hourglass shaped absorbent core which included 65% superabsorbent polymercomposition having a stepped capacity behavior and 35% commerciallyavailable softwood fiber. Comparative (control) absorbent articles had aconventional hour glass shaped absorbent core which included 65%commercially available superabsorbent material and 35% commerciallyavailable softwood fiber. The absorbent core dry density was 0.24 g/cm³and the absorbent articles each contained a 68 gsm intake layer (i.e.,surge layer). Twenty-four diapers were used each for both control (i.e.,comparative) codes, and for codes containing stepped capacitysuperabsorbent polymer compositions of the present invention. All codeswere tested on appropriately-size mannequins.

For each code, twelve absorbent articles were tested in the sittingposition and the remaining twelve articles were tested in the proneposition. For each position, fluid was added to half of the productsusing “female” mannequins and fluid was added to the remaining sixarticles using “male” mannequins. Two insulting protocols were employed,such that 12 products for each code were insulted using a “70/70/70”insult protocol (i.e., three insults of 70 ml each) and the remaining 12products for that code were insulted using a “35/70/70/70” protocol(i.e., four insults—one with 35 ml and then three with 70 ml each). Theinsult protocol is described in Table 10 below. The insult fluid (0.9 wt% aqueous sodium chloride solution) was kept at room temperature (about20° C.).

TABLE 10 Insult protocol for Example 4 70/70/70 Insult Scenario 1stInsult 1st Insult 2nd Insult 2nd Insult 3rd Insult 3rd Insult SubsequentPart 1 Part 2 Part 1 Part 2 Part 1 Part 2 4th Insult 5th Insult InsultsControl 45 ml of 25 ml of 45 ml of 25 ml of 45 ml of 25 ml of 70 ml of70 ml of 70 ml of 0.9% 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl0.9% NaCl 6% NaCl 6% NaCl NaCl Stepped 45 ml of 25 ml of 45 ml of 25 mlof 45 ml of 25 ml of 70 ml of 70 ml of 70 ml of 0.9% Capacity 8% NaCl 8%NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 2.67% 2.67% NaCl NaCl NaCl35/70/70/70 Insult Scenario 2nd Insult 2nd Insult 3rd Insult 3rd Insult4th Insult 4th Insult Subsequent 1st Insult Part 1 Part 2 Part 1 Part 2Part 1 Part 2 5th Insult 6th Insult Insults Control 35 ml of 45 ml of 25ml of 45 ml of 25 ml of 45 ml of 25 ml of 70 ml of 6% 70 ml of 6% 70 mlof 0.9% 0.9% 0.9% 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl NaCl NaCl 0.9%NaCl NaCl NaCl NaCl Stepped 35 ml of 45 ml of 25 ml of 45 ml of 25 ml of45 ml of 25 ml of 70 ml of 0.9% 70 ml of 70 ml of Capacity 8% NaCl 8%NaCl 8% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl NaCl 0.9% NaCl 0.9%NaCl 10 minute between insults 3 minutes between part 1 and 2 of insults

The absorbent articles were then insulted with the insult fluid asdescribed above until each product leaked. The load at leak was notedfor each product. The products were removed after the leak and werex-rayed, as described in Fluid Distribution Test described above tocalculate the wetted length and wetted area of liquid in the product.The average of the ratio of wetted length to load at leak and wettedarea to load at leak was calculated for each code. The results can beseen in Table 11 below.

TABLE 11 Average wetted length/load Average wetted area/load at leak atleak Code (cm/ml) (cm²/ml) Comparative 0.115 1.098 Example 4 (Control)Example 4 0.156 1.483 (Stepped Capacity)

It can be seen from Table 11 that absorbent articles of the presentinvention exhibit an improved fluid distribution when compared toarticles comprising conventional superabsorbent materials.

Example 5

Intake testing, as described in the Fluid Intake Rate Test above, wasperformed on absorbent cores. Codes included comparative examples(controls) with insulting fluid at room temperature (i.e., 0.9 wt %aqueous sodium chloride solution at about 20° C.); examples of theinvention (Stepped Capacity) with the same insulting fluid also at roomtemperature; and examples of the invention (Stepped Capacity) with thesame insulting fluid, but at a temperature of 50° C. All of theabsorbent cores had a conventional hour glass shape similar to those incommercial products, a dry density of about 0.24 gm/cm³, and were madewith 65% superabsorbent material (either commercially available SAP orthe superabsorbent polymer composition of the present invention) and 35%commercially available softwood fiber. The basis weight for eachabsorbent core was about 580 gsm. Each absorbent core was then insultedusing the insulting sequence described in the Fluid Intake Rate Testdescribed above. The specific liquids used for each portion of eachinsult series are indicated in Table 12 below.

TABLE 12 Temp 1^(st) Insult 1^(st) Insult 2^(nd) Insult 2^(nd) Insult3^(rd) Insult 3^(rd) Insult Code (° C.) Part 1 Part 2 Part 1 Part 2 Part1 Part 2 Comparative 20 45 gm of 25 gm of 45 gm of 25 gm of 45 gm of 25gm of Example 5 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9%NaCl (Control) Example 5-1 20 45 gm of 8% 25 gm of 8% 45 gm of 25 gm of45 gm of 25 gm of (Stepped NaCl NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9%NaCl Capacity) Example 5-2 50 45 gm of 8% 25 gm of 8% 45 gm of 25 gm of45 gm of 25 gm of (Stepped NaCl NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9%NaCl Capacity)

The intake rate, calculated based on the first part (45 gm) of eachinsult, can be seen in Table 13 below.

TABLE 13 Temp 1^(st) Intake Rate 2^(nd) Intake Rate 3^(rd) Intake RateCode (° C.) (gm/sec) (gm/sec) (gm/sec) Comparative 20 2.28 2.25 2.22Example 5 Example 5-1 20 1.97 2.09 1.11 Example 5-2 50 2.36 4.72 2.31

It can be seen from Table 13 that composites of the present inventionexhibit a generally similar intake rate than those utilizingconventional SAP. Also, a higher temperature tends to improve the intakerate for composites of the present invention.

Example 6

Intake testing, as described in the Fluid Intake Rate Test above, wasperformed on absorbent cores. Codes included a Control (ComparativeExample 6), representing composite that include conventional SAPs. Codesalso included a Stepped Capacity original (Example 6-1), SteppedCapacity Lite (Example 6-2) and Stepped Capacity X-Lite (Example 6-3),each of which represented composites in accordance with the invention,as identified in Table 14 below. All of the absorbent cores had aconventional hour glass shape similar to those in commercial products, adry density of about 0.24 gm/cm³, and were made with 65% superabsorbentmaterial (either commercially available SAP or superabsorbent polymercomposition of the present invention) and 35% commercially availablesoftwood fiber. The basis weight was about 580 gsm for all of the codes.Each absorbent core was then insulted using the insulting sequencedescribed in the Fluid Intake Rate Test above. The specific liquids usedfor each portion of each insult series are indicated in Table 14 below.

TABLE 14 Liquid 1st Insult 1st Insult 2nd Insult 2nd Insult 3rd Insult3rd Insult Temp. (deg C.) Part 1 Part 2 Part 1 Part 2 Part 1 Part 2 RoomControl 45 ml of 25 ml of 45 ml of 25 ml of 45 ml of 25 ml of 0.9% NaCl0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 60 C. Stepped Capacityoriginal 45 ml of 25 ml of 45 ml of 25 ml of 45 ml of 25 ml of 8% NaCl8% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 60 C. Stepped CapacityLite 45 ml of 25 ml of 45 ml of 25 ml of 45 ml of 25 ml of 5% NaCl 5%NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 50 C. Stepped CapacityX-Lite 45 ml of 25 ml of 45 ml of 25 ml of 45 ml of 25 ml of 2.67% 2.67%0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl NaCl NaCl

Intake Rate testing, as described in the Fluid Intake Rate Testprocedure above, was performed on all codes of the absorbent cores(Control, Stepped Capacity original, Stepped Capacity Lite and SteppedCapacity X-Lite). The insulting protocol consisted of 3 insults of 70ml, each split into two parts of 45 grams and 25 grams. The hold timebetween each insult group was 15 minutes (i.e., the time between theprevious 45 g/25 g insult and the subsequent 45 g/25 g insult), and timebetween two parts of each insult was 2 minutes (i.e., the time betweenthe 45 g insult and the 25 g insult).

The intake rate, calculated based on the first part (45 gm) of eachinsult, is listed in Table 15 below.

TABLE 15 2^(nd) Intake 1^(st) Intake Rate Rate 3^(rd) Intake Rate Code(gm/sec) (gm/sec) (gm/sec) Comparative Example 6 2.04 2.40 1.92(Control) Example 6-1 (Stepped 1.35 1.70 1.15 Capacity original) Example6-2 (Stepped 1.64 2.77 1.86 Capacity Lite) Example 6-3 (Stepped 1.931.65 1.67 Capacity X-Lite)

It can be seen from Table 15 that composites of the present inventionexhibit a generally similar intake rate compared to those utilizingconventional SAP.

Example 7

Static Mannequin testing, as described in the Mannequin Test Procedureabove was performed using absorbent articles in the form of a diaper.Each absorbent article of the present invention had a conventional hourglass shaped absorbent core which included 65% superabsorbent polymercomposition having a stepped capacity behavior and 35% commerciallyavailable softwood fiber. Comparative (control) absorbent articles had aconventional hour glass shaped absorbent core which included 65%commercially available superabsorbent material and 35% commerciallyavailable softwood fiber. Each absorbent core dry density was 0.24 g/cm³and each absorbent article contained a 68 gsm intake layer (i.e., surgelayer). Twelve articles were used for each of the following codes:Control (Comparative Example 7), Stepped Capacity original (Example7-1), Stepped Capacity Lite (Example 7-2) and Stepped Capacity X-Lite(Example 7-3).

For each code, all of the articles were tested in the prone positionwith liquid added using “male” mannequins. Two insulting protocols wereemployed, such that 6 products for each code were insulted with“70/70/70” insult protocol (i.e., three insults of 70 ml each) and theremaining 6 products for that code were insulted with “35/70/70/70”protocol (i.e., four insults—one with 35 ml and then three with 70 mleach). The hold time between each insult group was 15 minutes (i.e., thetime between the previous 45 g/25 g insult and the subsequent 45 g/25 ginsult), and time between two parts of each insult was 2 minutes (i.e.,the time between the 45 g insult and the 25 g insult).

The insult protocol is described in Table 16 below.

TABLE 16 70/70/70 Insult Scenaro 1st Insult 1st Insult 2nd Insult 2ndInsult 3rd Insult 3rd Insult Subsequent Liquid Temp. (deg C.) Part 1Part 2 Part 1 Part 2 Part 1 Part 2 Insults Room Control 45 ml of 25 mlof 45 ml of 25 ml of 45 ml of 25 ml of 70 ml of 0.9% 0.9% NaC 0.9% NaCl0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl NaCl 60 C. Stepped Capacity 45ml of 25 ml of 45 ml of 25 ml of 45 ml of 25 ml of 70 ml of 0.9%original 8% NaCl 8% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl NaCl 60C. Stepped Capacity Lite 45 ml of 25 ml of 45 ml of 25 ml of 45 ml of 25ml of 70 ml of 0.9% 5% NaCl 5% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9%NaCl NaCl 50 C. Stepped Capacity X-Lite 45 ml of 25 ml of 45 ml of 25 mlof 45 ml of 25 ml of 70 ml of 0.9% 2.67% 2.67% 0.9% NaCl 0.9% NaCl 0.9%NaCl 0.9% NaCl NaCl NaCl NaCl 35/70/70/70 Insult Scenario Liquid Temp.2nd Insult 2nd Insult 3rd Insult 3rd Insult 4th Insult 4th InsultSubsequent (deg C.) 1st Insult Part 1 Part 2 Part 1 Part 2 Part 1 Part 2Insults Room Control 35 ml of 45 ml of 25 ml of 45 m of 25 ml of 45 mlof 0.9% 25 ml of 70 ml of 0.9% 0.9% NaCl 0.9% NaCl 0.9% NaCl 0.9% NaCl0.9% NaCl NaCl 0.9% NaCl NaCl 60 C. Stepped Capacity 35 ml of 45 ml of25 ml of 45 m of 25 ml of 45 ml of 0.9% 25 ml of 70 ml of 0.9% original8% NaCl 8% NaCl 8% NaCl 0.9% NaCl 0.9% NaCl NaCl 0.9% NaCl NaCl 60 C.Stepped 35 ml of 45 ml of 25 ml of 45 m of 25 ml of 45 ml of 0.9% 25 mlof 70 ml of 0.9% Capacity Lite 5% NaCl 5% NaCl 5% NaCl 0.9% NaCl 0.9%NaCl NaCl 0.9% NaCl NaCl 50 C. Stepped 35 ml of 45 ml of 25 ml of 45 mof 25 ml of 45 ml of 0.9% 25 ml of 70 ml of 0.9% Capacity X-Lite 2.57%2.57% 2.57% 0.9% NaCl 0.9% NaCl NaCl 0.9% NaCl NaCl NaCl NaCl NaCl

The insult fluid (0.9 wt % aqueous sodium chloride solution) was set atroom temperature (˜20° C.) for the Control; at 60° C. for both SteppedCapacity original and Stepped Capacity Lite, and 50° C. for SteppedCapacity X-Lite. The absorbent articles were then insulted with theinsult fluids as described above until each product leaked. The load atleak was noted for each product. The products were removed after theleak and were x-rayed, as described in Fluid Distribution Test describedabove to calculate the wetted area of liquid in each product. Theaverage of the ratio of wetted area to load at leak was calculated foreach code, and is listed in Table 17 below.

TABLE 17 Average wetted area/load at leak Code (cm²/ml) ComparativeExample 7 (Control) 1.07 Example 7-1 (Stepped Capacity 1.46 original)Example 7-2 (Stepped Capacity Lite) 1.40 Example 7-3 (Stepped CapacityX-Lite) 1.20

It can be seen from Table 17 that the composites of the presentinvention (Stepped Capacity original, Stepped Capacity Lite, and SteppedCapacity X-Lite) result in longer wetted length per gm of liquid loadingcompared to a composite having conventional SAP. This demonstrates thatinvention results in better liquid wicking/distribution.

Example 8

The Swelling Rate of superabsorbent materials, such as those used in theExamples above, were measured as described in the Swelling Rate Testdescribed above. Various salt concentrations and temperatures were usedto measure the influence of these two characteristics on the SwellingRate. The results of the testing are summarized in Table 18 below.

TABLE 18 NaCl concentration of Temperature (° C.) test fluid (%)Swelling Rate (cm²/sec) 22 0.9 1.66 50 0.9 3.39 60 2.0 3.14 60 3.3 2.5060 5.0 2.00

It can be seen from Table 18 that Swelling Rate increases withincreasing temperature, and decreases with increasing salt (NaCl)concentration.

It will be appreciated that details of the foregoing examples, given forpurposes of illustration, are not to be construed as limiting the scopeof this invention. Although only a few exemplary embodiments of thisinvention have been described in detail above, those skilled in the artwill readily appreciate that many modifications are possible in theexamples without materially departing from the novel teachings andadvantages of this invention. For example, features described inrelation to one example may be incorporated into any other example ofthe invention.

Accordingly, all such modifications are intended to be included withinthe scope of this invention, which is defined in the following claimsand all equivalents thereto. Further, it is recognized that manyembodiments may be conceived that do not achieve all of the advantagesof some embodiments, particularly of the desirable embodiments, yet theabsence of a particular advantage shall not be construed to necessarilymean that such an embodiment is outside the scope of the presentinvention. As various changes could be made in the above constructionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

1. An absorbent composition comprising: a superabsorbent polymercomposition having an initial absorbent capacity of at least about 5grams saline per gram of superabsorbent polymer composition; and a firsttriggering mechanism having a first release time of between about 5 and60 minutes; wherein the superabsorbent polymer composition has a secondabsorbent capacity of at least about 25% greater than the firstabsorbent capacity as measured by the mCRC Test; a second triggeringmechanism having a second release time of between about 10 and 120minutes and at least about 5 minutes longer than the first release time;wherein the superabsorbent polymer composition has a third absorbentcapacity of at least about 25% greater than the second absorbentcapacity as measured by the mCRC Test.
 2. The absorbent composition ofclaim 1 further comprising: a third triggering mechanism having a thirdrelease time of between about 15 and 180 minutes and at least about 5minutes longer than the second release time; wherein the superabsorbentpolymer composition has a fourth absorbent capacity of at least about25% greater than the third absorbent capacity as measured by the mCRCTest.
 3. The absorbent composition of claim 2 further comprising: afourth triggering mechanism having a fourth release time of betweenabout 20 and 240 minutes and at least about 5 minutes longer than thethird release time; wherein the superabsorbent polymer composition has afifth absorbent capacity of at least about 25% greater than the fourthabsorbent capacity as measured by the mCRC Test.
 4. The absorbentcomposition of claim 1 wherein the swelling rate of the superabsorbentpolymer composition has a swelling rate that is at least about 20%greater than the swelling rate of a conventional superabsorbent materialas measured by the Swelling Rate Test.
 5. The absorbent composition ofclaim 4 wherein the swelling rate of the superabsorbent polymercomposition has a swelling rate that is at least about 50% greater thanthe swelling rate of a conventional superabsorbent material as measuredby the Swelling Rate Test.
 6. The absorbent composition of claim 5wherein the swelling rate of the superabsorbent polymer composition hasa swelling rate that is at least about 100% greater than the swellingrate of a conventional superabsorbent material as measured by theSwelling Rate Test.
 7. An absorbent composite comprising: awater-insoluble fibrous matrix; a superabsorbent polymer compositionhaving an initial absorbent capacity of at least about 5 grams salineper gram of superabsorbent polymer composition; and a first triggeringmechanism having a first release time of between about 5 and 60 minutes;wherein the superabsorbent polymer composition has a second absorbentcapacity of at least about 25% greater than the first absorbent capacityas measured by the mCRC Test; a second triggering mechanism having asecond release time of between about 10 and 120 minutes and at leastabout 5 minutes longer than the first release time; wherein thesuperabsorbent polymer composition has a third absorbent capacity of atleast about 25% greater than the second absorbent capacity as measuredby the mCRC Test.
 8. The absorbent composite of claim 7 wherein thesuperabsorbent polymer composition further comprises: a third triggeringmechanism having a third release time of between about 15 and 180minutes and at least about 5 minutes longer than the second releasetime; wherein the superabsorbent polymer composition has a fourthabsorbent capacity of at least about 25% greater than the thirdabsorbent capacity as measured by the mCRC Test.
 9. The absorbentcomposite of claim 8 wherein the superabsorbent polymer compositionfurther comprises: a fourth triggering mechanism having a fourth releasetime of between about 20 and 240 minutes and at least about 5 minuteslonger than the third release time; wherein the superabsorbent polymercomposition has a fifth absorbent capacity of at least about 25% greaterthan the fourth absorbent capacity as measured by the mCRC Test.
 10. Theabsorbent composite of claim 8 wherein the swelling rate of thesuperabsorbent polymer composition has a swelling rate that is at leastabout 20% greater than the swelling rate of a conventionalsuperabsorbent material as measured by the Swelling Rate Test.
 11. Theabsorbent composite of claim 10 wherein the swelling rate of thesuperabsorbent polymer composition has a swelling rate that is at leastabout 50% greater than the swelling rate of a conventionalsuperabsorbent material as measured by the. Swelling Rate Test.
 12. Theabsorbent composite of claim 11 wherein the swelling rate of thesuperabsorbent polymer composition has a swelling rate that is at feastabout 100% greater than the swelling rate of a conventionalsuperabsorbent material as measured by the Swelling Rate Test.